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Condensed-Matter Physics (1986)

Chapter: I Highlights, Opportunities, and Needs

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Suggested Citation:"I Highlights, Opportunities, and Needs." National Research Council. 1986. Condensed-Matter Physics. Washington, DC: The National Academies Press. doi: 10.17226/628.
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I Highlights, Oand Needs The focus in this volume is solely on condensed- matter physics, which is the foundation of a significant portion of the broader field of materials science, and the dividing line between the two fields is not always a sharp one. However, we are not surveying materials science nor the considerable impact of condensed- matter physics on technology. The interface between physics and technology will receive fuller treatment in another volume in this survey.

HIGHLIGHTS, OPPOR TUNI TIES, AND NEEDS 3 CONDENSED-MATTER PHYSICS AND ITS IMPORTANCE Condensed-matter physics is the fundamental science of solids and liquids, states of matter in which the constituent atoms are sufficiently close together that each atom interacts simultaneously with many neighbors. It also deals with states intermediate between solid and liquid (e.g., liquid crystals, glasses, and gels), with dense gases and plasmas, and with special quantum states (superfluids) that exist only at low temperatures. All these states constitute what are called the condensed states of matter. Condensed-matter physics is important for two reasons. The first is that it provides the quantum-mechanical foundation of the classical sciences of mechanics, hydrodynamics, thermodynamics, electronics, optics, metallurgy, and solid-state chemistry. The second is the mas- sive contributions that it provides to high technology. It has been the source of such extraordinary technological innovations as the transis- tor, superconducting magnets, solid-state lasers, and highly sensitive detectors of radiant energy. It thereby directly affects the technologies by which people communicate, compute, and use energy and has had a profound impact on nonnuclear military technology. At the fundamental level, research in condensed-matter physics is driven by the desire to understand both the manner in which the building blocks of condensed matter-electrons and nuclei, atoms and molecules combine coherently in enormous numbers (~1024/cm3) to form the world that is visible to the naked eye, and much of the world that is not, and the properties of the systems thus formed. It is in the fact that condensed-matter physics is the physics of systems with an enormous number of degrees of freedom that the intellectual challenges that it presents are found. A high degree of creativity is required to find conceptually, mathematically, and experimentally tractable ways of extracting the essential features of such systems, where exact treat- ment is an impossible task. Condensed-matter physics is intellectually stimulating also because of the discoveries of fundamentally new phenomena and states of matter, the development of new concepts, and the opening up of new subfields that have occurred continuously throughout its 60-year history. It is the field in which advances in quantum and other theories most directly confront experiment and has repeatedly served as a source or testing ground for new conceptual ways of viewing complex systems. In fact, condensed-matter physics is unique among the various subfields of physics in the frequency with which it feeds its fundamental ideas into other areas of science. Thus, advances in such

4 HIGHLIGHTS, OPPORTUNI TIES, AND NEEDS subareas of condensed-matter physics as many-body problems, critical phenomena, broken symmetry, and defects have had a major impact on nuclear physics, elementary-particle physics, astrophysics, molecular physics, and chemistry. These advances continue and over the promise of equally fundamental discoveries in the next decade. At the same time, condensed-matter physics excites interest because of the well-founded expectations for applications of discoveries in it. Of all the branches of physics, condensed matter has the greatest impact on our daily lives through the technological developments to which it gives rise. Such familiar devices as the transistor, which has led to the miniaturization of a variety of electronic appliances; the semiconductor chip, which has made possible all the myriad aspects of the computer; magnetic tapes used in recording of all kinds; plastics for everything from kitchen utensils to automobile bodies; catalytic con- verters to reduce automobile emissions; composite materials used in fan jets and modern tennis rackets; and NMR tomography are but a few of the practical consequences of research in condensed-matter physics. A whole new technology, optical communications, is being developed at this time from research in condensed-matter physics, optics, and the chemistry of optical fibers. These examples serve to illustrate the intimate connection between fundamental science and the development of basic new technology in condensed-matter physics. In both universities and industry they are carried out by people with the same research training, who use the same physics concepts and the same advanced instrumentation. Be- cause fundamental science in condensed-matter physics is so deeply involved with technological innovation, it has a strong natural bond with industry. This is the main reason why condensed-matter physics has been so successful in leading industrial innovation. Indeed, the full extent to which the consequences of research in condensed-matter physics play a role in the quality of our everyday lives, and in meeting national needs, is far greater than any such listing can indicate. In order to show this explicitly we have constructed the matrix displayed in Table 1, the first column of which lists the subareas of condensed-matter physics, and the first row the major areas of human and technological activity that are of national interest. The elements of the matrix are filled in with a solid circle, indicating a critical connection between the corresponding subarea of condensed- matter physics and the area of application; a half-filled circle, indicating an important or emerging connection; an open circle, denoting the possibility of a connection; or a blank, implying that the connection is not known. In Appendix A this matrix is repeated, but with qualitative

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6 HIGHLIGHTS, OPPORTUNITIES, AND NEEDS comments concerning the connections replacing the various circles. This table makes the point graphically that condensed-matter physics plays an indispensable role in the maintenance of the quality of our daily life and in providing for national security. DISCOVERY The 1 950s saw such achievements as the rapid development of semiconductor technology after the discovery of the transistor; the rise of many-body theory (the application of the methods of quantum field theory to large and complex systems) as a field of theoretical physics, and its crowning achievement, the solution of the 50-year-old problem of superconductivity; the heyday of magnetic resonance methods in physics; and the elucidation of the Fermi surfaces of metals. The 1960s saw the discovery of high critical fields and superconducting magnets, as well as of the Josephson erect and other electron tunneling methods and devices; the construction of the first working lasers and further giant strides in laser physics; the initial explanation of the ancient problem of the resistance minimum by Kondo and the opening up of a whole new physics of similar Fermi-surface effects in metals such as the x-ray edge; the development of pseudopotential and density functional methods, among others, that have made electronic structure calculations almost routine; and the initial development of high-energy probe methods for the study of electronic structure such as ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectros- copy (XPS). From time to time, there have been those who have predicted the end of this era of discovery. Remarkably, the subject continues to produce surprises. In what follows we present a selection of some of the most interesting advances in condensed-matter physics that oc- curred in the 1970s and early 1980s. Artificially Structured Materials One area of condensed-matter physics that has progressed remark- ably in the past decade is that of artificially structured materials- materials that have been structured either during or after growth to have dimensions or properties that do not occur naturally. The most important techniques for the creation of such materials are molecular-beam epitaxy (MBE), the molecule-by-molecule deposition of material of the desired composition from a molecular beam' and

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 7 metallo-organic chemical vapor deposition (MOCVD). These are prime examples of technological breakthroughs, used primarily to make semiconductor lasers and other devices, feeding back to fundamental physics. One can fabricate artificial periodic superlattices consisting of alternating layers of different semiconductors, different metals, or semiconductors and metals, and one can also create artificial, purely two-dimensional electron gases. The latter have unique and important properties, e.g., extremely high electron mobilities, which cannot be provided by metal-oxide-semiconductor (MOS) inversion layers. The new physical phenomena to which the resulting structures have given rise include the quantized Hall effect and the fractionally quantized Hall effect. It has also been possible to grow metallic superlattices in which the electronic mean free path is appreciably longer than the period of the superlattices (the sum of the thicknesses of the two alternating metal layers). It is found that it is possible to induce new lattice structures rather easily in such superlattices. Metal/insu- lator superlattices are ideal systems for the study of dimensional effects in metals, e.g., the crossover from two- to three-dimensional superconductivity in Nb/Ge superlattices as the Ge thickness is de- creased. The Quantized Hall Eject Modern technology has made possible unique, purely two- dimensional electron gases (in the sense that only one quantum state is excited in the direction perpendicular to the plane of the gas, so that electronic motion in it is strictly confined to that plane). These systems show exciting properties and are a new laboratory for the study of fundamental physics. The most remarkable property of such systems is undoubtedly the quantized Hall eject. At low temperature and high perpendicular magnetic field, the electron states are split into so-called Landau or cyclotron energy levels. It is found that when the Fermi level is between two such levels one sees an almost perfectly flat plateau or constant value of the Hall conductance, the conductance perpendicular to the electric and magnetic fields, as well as zero parallel conductance. These plateaus are found to be quantized in units of e21h = 1/25,812.8 ohm-~. The precision of this result, at least one part in a hundred million, has led to improvement in the measurement of this fundamental constant and to a new portable resistance standard. More recently, quantization of the Hall conductance in simple fractions like 1/3, 2/5, and 2/7 of e21h has been seen, and an explanation of this

8 HIGHLIGHTS. OPPORTUNITIES, AND NEEDS effect has been proposed, and widely accepted, that involves a completely new and unexpected ordered state of matter. In this state one proposes that a new type of elementary excitation with fractional electronic charge plays a major role. Ejects of Reduced Dimensionality For many years condensed-matter theorists studied one- and two- dimensional models of solids because it was often possible to obtain exact results there where the corresponding, physical, three-dimen- sional models were intractable. The existence of such exact solutions in low-dimensional systems has prompted experimentalists to search, successfully, for physical systems whose physical properties agree well with those of one- and two-dimensional theoretical models. These include quasi-one-dimensional magnetic systems composed of chains of magnetic atoms, separated from each other by nonmagnetic atoms, and quasi-two-dimensional systems realized by layered compounds, such as graphite intercalation compounds, in which atomic layers are widely separated and weakly interacting. Other examples have arisen either out of technological discoveries or from the synthesis of interesting new materials. The inversion layers used in the quantized Hall effects are an example of reduced dimen- sionality systems important in technology, an example that has been vital to the physics of disordered systems as well. Another is the development of methods for studying adsorbed layers on surfaces that undergo phase transitions of typically two-dimensional type. A third is the discovery of methods for making freely suspended layers of a liquid crystal one or a few molecules thick. New materials showing metallic properties in only one or two dimensions have been synthesized, for instance the transition-metal dichalcogenides, which can be cleaved to produce single layers or intercalated with large molecules that separate the layers by large distances, and a number of organic one-dimensional chain metals such as polyacetylene. These various developments have encouraged ex- perimentalists and theorists to think of dimensionality as a new free parameter. Charge-Density Waves Among phenomena that are most clearly demonstrated in low- dimensionality systems are charge (or in some cases spin) density waves. A few isolated cases in which the structure of a solid was

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 9 modulated periodically had been known for decades, but it was not until modern low-dimensionality materials became available, such as the dichalcogenides and trichalcogenides of Nb and other transition metals, and some organic metals, such as polyacetylene and tetra- thiafulvalene-tetracyanoquinodimethane (TTF-TCNQj, that the phe- nomenon could be studied in general. Theory has predicted for many years that such materials should show density waves especially easily. In such materials the structure contains two periods that may be incommensurate, hence giving an overall nonperiodic structure. A particularly important possibility is the sliding of such an incommen- surate wave through the parent lattice, a new phenomenon illustrating in a clean microscopic model the age-old effects of sliding and sticking friction. The materials that display these ejects, e.g., NbSe3 and TaS3, are remarkable quantum systems with the richness of superconductiv- ity and should be excellent for studying various aspects of macroscopic quantum phenomena. Other interesting phenomena relate to defects in these waves, which have strange topological properties, fractional charge per unit area, and, in the case of polyacetylene, strange spin and charge properties. This subject continues to be actively discussed, not only because of its scientific interest but also because of its possible technical interest. Disorder It is only within the past decade that physicists have begun to focus on the problems intrinsic to disordered states of matter such as random alloys, glass, and gels. Historically they had dealt with such systems- often effectively by trying to average out the disorder in the most efficient possible way, to produce an '`effective medium." Now they have begun to look for intrinsic properties of disordered materials. The most striking of these is localization, the tendency to form quantum states that cannot move except with the help of thermal energy. Experimentally, the study of localization is much clarified by using a two-dimensional geometry, in which one often sees a unique nonclas- sical behavior of the electronic conductivity, and by technical ad- vances in microfabrication, which allow the study of effectively one-dimensional wires and of tiny loops that show strange conductivity -oscillations in a magnetic field. A second disordered material of technical importance is glass; the glass transition and the high- temperature annealing properties of glass remain almost completely mysterious, but a whole new physics has grown up around a new entity recently discovered in the low-temperature behavior of glass, the

10 HIGHLIGHTS, OPPORTUNITIES, AND NEEDS so-called tunneling centers. The structure of glass is also a great mystery; the computer may help in deciphering it, but in fact we know so little that we do not yet even believe we can program a computer to make a viable model of glass. Mixed Valence and Heavy Fermions It is not uncommon, the chemists have found, for the same chemical element to exhibit two valences in the same compound as, for example, magnetite, which contains both ferrous and ferric iron at different atomic positions. On the other hand, metals such as nickel do not necessarily have a fixed valence, as the electrons move freely through the lattice. The rare-earth metals, however, normally have a fixed valence for the inner f electrons, which can be identified because they show magnetic properties identical to those of ions in an insulating salt. It now appears that there is a large class of compounds based on the rare-earth atoms Ce, Sm. Eu, Tm, Yb, and now the actinide element U. that are intermediate between these two cases in an unusual way. Some types of measurements one-electron probes, x-ray edges show both valences simultaneously developed on the same atom. Other types of measurement, such as those of low-temperature magnetism or conductivity, show a fixed valence, sometimes interme- diate and sometimes not. It appears that electrons are quantum mechanically tunneling rather slowly in and out of the f shells, with very exotic results, such as electron bands with effective electron masses as large as 1000 times a normal electron mass, which nonethe- less exhibit superconductivity at very low temperatures. Present speculation is that these superconductors are of a totally new type, and are analogous to superfluid 3He. The valence fluctuations in other materials lead to a number of other fascinating effects: metal/insulator transitions, magnetic/nonmagnetic transitions, soft (highly compress- ible) lattices, and transitions into exotic magnetic ground states. A full explanation of these phenomena might have far-reaching consequences for our understanding of magnetism and bonding in solids. The Superfluid Phases of 3He A high point in research in condensed-matter physics of the last decade was the discovery that 3He is a superfluid (i.e., can flow without resistance through narrow channels) at temperatures below 3 mK. This is the first, and only, new superfluid to be discovered since the

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 11 superfluidity of 4He was established in 1937. The properties of 3He are very different from those of 4He because 4He obeys the quantum- mechanical laws of Bose statistics, whereas 3He obeys Fermi statistics, the same as electrons. At the same time, superfluid 3He displays a rich variety of physical properties in addition to those possessed by the previously known superfluids. This is because the interaction between pairs of helium atoms that is responsible for the superfluidity of 3He is qualitatively different from the interaction between pairs of electrons responsible for the superconductivity of all the currently known superconductors. In particular the superfluid is locally anisotropic, acting as though it was made up of molecules with internal rotational motions about a specific direction. Several major advances in condensed-matter physics were fueled primarily by new theoretical concepts. Descriptions of two of them follow. The Renormalization Group Methods These techniques are useful in dealing with physical phenomena in which there exist fluctuations that occur simultaneously over a wide range of different length, energy, or time scales. The method proceeds by stages, in which one successively discards the shortest-wavelength fluctuations until a few macroscopic degrees of freedom remain. The effects of the short-wavelength fluctuations are taken into account approximately at each stage by a renormc~lizc~tion, i.e., change in magnitude, of the interactions among the remaining long-wavelength modes. These techniques were developed initially in particle physics but came into their own in the theory of phase transitions, the branch of condensed-matter physics that deals with changes of state, such as the melting and freezing of solids and liquids and the magnetization of ferromagnets. Their use has provided a theoretical understanding of empirical relations among different properties near the phase transition or critical point of a given system and has made it possible to predict critical properties with a high degree of accuracy. These predictions have been confirmed by a wide variety of subsequent experiments. The renormalization group techniques have found applications in such diverse areas of condensed-matter physics as disordered electronic systems, impurity problems, disordered magnetic materials called spin glasses, nonlinear dynamical systems, long polymer chains, and per- colation through macroscopically inhomogeneous systems such as porous rocks.

12 HIGHLIGHTS, OPPORTUNITIES, AND NEEDS Chaotic Phenomena in Time and Space A second new subfield of condensed-matter theory has arisen from our overlapping interests with the fields of hydrodynamics and plasma physics in strongly driven systems, systems so far from equilibrium that linear equations no longer hold. A bewildering variety of phenom- ena can appear from the simplest models of these systems, which attempt to describe them in terms of one or a few degrees of freedom: singly or doubly periodic motions, or purely chaotic ones, arising entirely from the internal dynamics with no random external inDu- ences. Some remarkable universality properties appear in such sys- tems and are exhibited under some experimental conditions. Many focuses of debate remain: for instance, it is clear that fully developed turbulence cannot be described by such simple mathematics, but how far can such a simple approach go toward providing a description? What is the criterion that determines the remarkable patterns that often appear in such systems? We have learned how complex the simplest sets of equations describing a few modes can be- how far do we have to go to describe a realistic system like a real laser or a solidifying liquid? Chaotic nonlinear behavior is common to a wide variety of condensed-matter systems, such as semiconducting lasers and various superconducting devices, as well as the much studied hydrodynamic systems. Finally, some new areas have resulted from experimental break- throughs. Some of these are discussed below. Widespread Use of Synchrotron Radiation Synchrotron radiation is electromagnetic radiation emitted from particle accelerators by charged particles (usually electrons) with large energy in the range from hundreds of MeV to 10 GeV or more. Synchrotron sources provide intense radiation at wavelengths for which laser sources are either unavailable or not yet tunable. Because synchrotron radiation has a number of desirable characteristics, e.g., high brightness, wide tunability, strong collimation, linear polarization, stability, and the fact that the radiation often occurs in ~0. 1-1 nanosecond pulses, in the past 10 years this waste product of particle physics has been used increasingly for low-energy physics in a broad range of fields. In condensed-matter physics, synchrotron radiation has been used to determine experimentally the energy-momentum relation E(k) for electrons in such elements as Cu and Ni and such semicon- ductors as GaAs and CdS; the inadequacy of a purely band model of

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 13 ferromagnetism in nickel has been demonstrated by an experimental determination of the temperature dependence of the exchange splitting; an understanding of the fundamental problem of two-dimensional melting and wetting has been gained through experiments employing synchrotron radiation; the structure of glassy amorphous materials has been investigated in this fashion, and phase transitions in few- molecule-thick layers of liquid crystals have been studied; and the oxidation state and local geometries of molecules adsorbed on surfaces and studies of catalytic activity at surfaces and of the structures of the surfaces themselves have been carried out. A great deal of synchrotron radiation work has been carried out on the formation of semiconductor- oxide, semiconductor-semiconductor, and semiconductor-metal inter- faces; synchrotron radiation has also been used in lithography to produce artificial structures with dimensions as small as 70 A. Syn- chrotron radiation today stands as one of the most versatile tools available to experimentalists in a broad range of fields. Atomic Resolution Experimental Probes A major advance of the past decade in instrumentation for experi- mental studies of condensed matter was the development of several probes capable of seeing individual atoms. One of these is the scanning vacuum tunneling microscope. In this instrument a sharp metal tip is placed at a distance of ten or so angstroms above a solid surface, with a potential difference between the tip and the surface. Electrons can transfer from one to the other via quantum-mechanical tunneling, and the resulting electric current is sensitive to the distance from the tip to the sample. As the tip is scanned across the surface the height of the surface at each point can be determined from the current fluctuations. In particular, bumps in the surface electron density produced by individual atoms can influence the current, as can steps and other defects. Thus with this instrument one now has the possibility of determining the structure by direct observation. Also developed in the past decade are new electron microscopes that can be used to image defects within the bulk of a crystal. By 1982 the resolution of com- mercial transmission electron microscopes had reached about 1.5 A. Since the beam passes through the entire sample, electron microscopy is naturally adapted to the study of linear and planar defects aligned with the beam. Atomic positions in perfect crystals can also be obtained through the use of thin-film samples. A related atomic resolution probe is the scanning transmission electron microscope whose current resolution is about 2 A. Heavy atoms located on carbon

14 HIGHLIGHTS. OPPORTUNITIES, AND NEEDS films have been imaged individually by this probe. We can expect that in the future these kinds of probe will be used more and more for direct determination of atomic positions within and on the surfaces of solids. RESEARCH OPPORTUNITIES IN CONDENSED-MATTER PHYSICS IN THE NEXT DECADE The list of outstanding achievements during the past decade given in the previous section demonstrates the vitality of condensed-matter physics and is a strong indication of progress to be made in the coming decades. Many of the developments provide new experimental or theoretical tools for studying physical problems that are as yet un- solved. As examples, we cite the applications of vacuum tunneling microscopy and of intense synchrotron radiation sources, as well as the various renormalization-group methods of theoretical analysis. There are newly discovered materials or phenomena that are only partially understood and that therefore open up new fields of inquiry. Examples here include the heavy-fermion superconductors, modulated semicon ductor structures, the quantized and fractionally quantized Hall effect, and the random magnetic-field problem. In the remainder of this section we describe some of the areas of condensed-matter physics that appear to us to provide particularly exciting research opportunities in the next decade. In compiling such a list, we are, however, cognizant of the fact that each of the preceding two or three decades has seen the discovery of physical phenomena or methods that could not have been predicted at the beginning of that decade. For example, several of the outstanding discoveries listed in the previous section, such as the new phases of 3He and the quantized Hall effect, would have been absent from a list of opportunities drawn up in 1970. It is virtually certain that the coming decade will have its share of such unexpected discoveries. A great deal of effort is expected to be devoted to the determination of the structures and excitations of surfaces of crystalline solids, both clean and covered with adsorbed layers, and of the interfaces between two different solids and between solids and liquids. These investiga- tions will be carried out by the use of such instruments and techniques as the recently developed scanning vacuum tunneling microscope, Rutherford ion backscattering, grazing-incidence x-ray scattering, low- energy electron diffraction, electron energy loss spectroscopy, and atomic diffraction. The results of these determinations are crucial to a detailed understanding of various surface and interface excitations, electronic, vibrational, and magnetic. We can hope that eventually we

HIGHLIGHTS, OPPORTUN/TIkS AND NEkDS 15 may not only determine surface structures, but control them by deliberate doping or other physical and chemical techniques. The great goal of understanding catalysis must always remain in our minds, but few experiments yet undertaken approach the real problems of catal- ysis in practical systems as opposed to atomically clean models. The determination of the structure, ground-state properties, and elementary excitations in glasses, amorphous materials, and other disordered systems both magnetic and nonmagnetic will be an active area of research, because of both the interesting physical properties displayed by such systems and the technological importance of many of them. There is certain to be a vigorous effort in developing new types of disordered materials for electronic and optical applications. The interplay of this field with computer science and even more distant fields such as neurobiology is a fascinating new development that is sure to be a major area of activity in the next decade. Here, for the first time, physics is pushing at the theoretical limits of computa- tional complexity, and hence it is not even clear that meaningful simulation of the structure of glass, or even the folding of a random polymer or protein molecule, for example, can be carried out in principle without recourse to completely new ideas in the computer field and new and complex theoretical concepts. We may also assume that new physical and chemical insights will be necessary in this area, especially as we approach problems involving even more complicated materials such as polymer glasses and gels. Artificially structured materials can be ordered in their structure, as in the case of artificial superlattices, or they can be ordered on a microscopic scale and yet be disordered overall, as in the cases of systems composed of small particles of one material embedded in a matrix of a second. Such materials possess transport, elastic, and optical properties that can differ considerably from those of their constituents in the bulk state, and, perhaps more importantly, these properties can be tuned in desirable ways by varying the constituents and their thicknesses in the case of superlattices or by altering the constituents, their size distributions, and their relative concentrations in the case of mixed media. The length scales involved in artificially structured materials, however, are so small that many of the conven- tional methods of solid-state physics are no longer applicable in determining their physical properties. In this area interface states, ballistic transport, Kapitza resistance, quantum-well effects, noise, and electromigration and thermomigration are all topics of fundamental interest and will offer research opportunities for the future. In the area of phase transitions, we understand equilibrium phenom

16 HIGHLIGHTS, OPPORTUNITIES, AND NEEDS ena in principle very well, but the kinetics of phase transitions remains an important field of materials science, especially because of its practical value, as for example under the exotic conditions of laser pulse annealing. Kinetic questions may even underlie the problems of phase transitions in the early universe. The renormalization group will continue to expand beyond its classic uses into more or less exotic domains, as it has already enlightened studies of chaos and disorder. The last decade has seen the creation of new organic and polymeric materials with striking physical properties, among them metallic elec- trical conductivity and even superconductivity. Although a theoretical explanation of some of the properties of some of these materials is beginning to emerge, much remains to be understood, and opportuni- ties for good theoretical work in this field will continue to exist into the foreseeable future. The underlying physics of exotic new crystalline materials, such as heavy fermion conductors, charge-density wave materials, and high TC and HC2 superconductors such as the Chevrel phases, is expected to be elucidated in the coming decade. It has been shown repeatedly that as materials are subjected to more extreme physical conditions they display new physical properties. Thus, within the past decade the combination of small size, low temperature, and high magnetic fields made possible the discovery of the fractionally quantized Hall effect; the ability to reach ultralow temperatures made possible- the discovery of the superfluid phases of 3He; the use of very high pressures enabled the rare gas xenon to be solidified into a metal; the use of very low pressures (ultrahigh vacuum) has made possible the first efforts to determine structures of surfaces uncontaminated by unwanted foreign atoms or oxide layers. It is expected that the study of condensed matter at ever lower and higher temperatures, at higher magnetic and electric fields, at higher and lower pressures, and at much higher purities will continue into the next decade, with the range of properties of known materials being broad- ened thereby. In the field of nonlinear dynamics, instabilities, and chaos, many questions have been raised by the work of the past decade, and efforts to answer them will surely parallel the discovery of new phenomena in the next decade. We have already mentioned some of these, but a particularly important one is how to treat turbulence and instabilities in real systems with many degrees of freedom when we know that the dynamics of systems with only a few degrees of freedom is already incredibly complicated. The effect of sequences of instabilities on heat, mass, and momentum transport in fluids have not been adequately

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 17 studied and could have practical applications, e.g., in the understand- ing of lubrication. There is as yet no really fundamental understanding of the mechanisms that control solidification patterns in, for example, snowflakes, quenched alloys, or directionally solidified eutectic mix- tures. An important problem for the future is the computer simulation of the onset and growth of turbulence in hydrodynamic systems. Fundamental questions that remain to be answered include: Is chaos a meaningful concept in quantum mechanics? How does one character- ize and classify the steady states that are obtained under constant external conditions away from thermodynamic equilibrium? While our ability to calculate electronic structures in relatively simple situations with relatively weak interelectronic interactions, such as semimetals and semiconductors, has increased enormously, we still have great difficulties with a variety of types of strongly interacting systems. Theories of magnetic metals and the various types of metal- insulator transitions remain controversial. Even more primitive is our understanding of metals where the electron-phonon interaction is strong, such as the charge-density wave materials as well as the strong-coupled superconductors. Many as yet unexplained experimen- tal data exist. The same difficulties probably extend to many surface electronic states as well as to the newer organic and other linear compounds. The mixed valence problem promises to be an even more difficult one to understand. The methods of pseudopotential and density functional theory work well for chemically simple systems, but one hopes to extend electronic calculations at the same level of rigor and accuracy to chemically sophisticated systems such as organic compounds. Equally sophisti- cated molecular orbital methods may be within our grasp, but so far their exploitation has rested with more chemically oriented theorists. From liquid crystals one should expect that more complex mesophases will begin to be of importance in condensed-matter theory and experiment. A start has been made with Iyotropic liquid crystals and membrane phase transitions, for example, as well as with the physics of biologically interesting molecules such as proteins and nucleic acid chains. The next decade may be the decade in which the physics of random polymers becomes as interesting as more conven- tional disordered systems are now. Applications of femtosecond laser spectroscopy to studies of con- densed matter will increase in number and scope over the coming decade. Structural changes, such as melting and structural phase transitions, can now be studied in a time-resolved fashion on the femtosecond scale. The response of crystalline solids to short electrical

1 8 HI GHLI GHTS, OPPOR TUNI TIES, A ND NEEDS pulses can now also be studied by femtosecond spectroscopy. Efforts to create even shorter pulses will continue, in parallel with efforts to extend the wavelengths of such short pulses toward the ultraviolet and infrared regions. Free-electron lasers show great promise as high-power tunable sources. The first free-electron laser operated in the near infrared, and recently lasing action has been achieved in the blue region of the visible spectrum. Two that produce both far-infrared and infrared radiation are just coming into operation. The availability of such instruments will open the door to the experimental study of a wide variety of nonlinear optical phenomena in condensed matter. These include the generation of magnetic and vibrational excitations with wave vectors at arbitrary points of the first Brillouin zone of the corresponding crystals; driving a displacive ferroelectric crystal above its nominal transition temper- ature to induce the ferroelectric phase transition at this higher temper- ature; studying the pinning of charge-density waves in one-dimensional metals; and investigating the expected large nonlinear response of two-dimensional plasmons at semiconductor heterojunction interfaces. It is expected that epithermal neutrons produced by pulsed neutron sources will be used to study excitations in condensed matter whose energies exceed thermal energies and extend up into the electron-volt range. In addition, they will include time-dependent effects such as high-frequency vibrations in solids, particularly those containing hy- drogen atoms. It should also prove possible to measure in this way the momentum distribution of light atoms in their ground state. Of partic- ular interest in this regard is the superfluid 4He, for which a zero- momentum condensate fraction is presumed to exist but whose mag- nitude remains uncertain. We believe that the next decade will see the increased use of insertion devices (undulators and wigglers) to increase the brightness of synchrotron radiation sources. This development will make it possible, for example, to study the properties of defects in crystals in the 10-5-1 o-6 concentration range, in contrast with the 10-3-10-4 concentration range that can be studied at present. The higher resolu- tion in energy and momentum expected from the use of insertion devices will also make it possible to study small samples of materials that are difficult to prepare in the form of large crystals. Inelastic x-ray scattering from the bulk and from surfaces should become a reality, as well as the ability to determine experimentally electronic structures of solids, particularly of systems with small Brillouin zones, such as artificially structured materials and semiconductors with reconstructed surfaces.

HI GHLI GHTS, OPPOR TUNI TIES, A ND NEEDS 1 9 NEEDS OF CONDENSED-MATTER PHYSICS IN THE NEXT DECADE It is obvious that the significant new discoveries in condensed-matter physics described in the previous section will not appear spontane- ously. The question immediately arises: What will it take to produce them? To answer this question it is necessary first to describe briefly the changes that have occurred in the past decade in the directions of research in condensed-matter physics and the way it is done, which differs from the way research is done in other areas of physics. The nature of research in condensed-matter physics has changed throughout its history to embrace ever-more complex phenomena. Among its earliest triumphs in the post-World War 11 era was providing the basic understanding of high-technology materials (e.g., semicon- ductors, magnetic materials, and superconductors). Over the years the sophistication of condensed-matter theory has reached such a level that at least for elementary systems with almost perfect structures, such bulk properties as their cohesive, electronic, dynamic, thermal, optical, magnetic, and transport properties are now well understood. In recent times, the emphasis in condensed-matter physics has shifted toward materials with novel or special properties; to imperfect systems; toward problems relating to technologically or biologically important materials and structures; to bounded systems and ones with surfaces and interfaces; to those with remarkable states of electronic order; to strongly perturbed rather than equilibrium systems; and to disorder rather than order. As a consequence, with the aid of new instrumentation, new materials fabrication procedures, and the imagi- native use of the computer, condensed-matter physics is beginning to provide the basis for understanding the fundamental properties of systems that are still more interesting than the classical ones from a scientific and technological point of view. Research in condensed-matter physics differs from research in some other areas of physics in a way that is fundamental for determining priorities in support for it: it is carried out almost entirely by individ- uals or by small groups of researchers. This is indicated in Figure 1, where a histogram is plotted showing the number of papers published in condensed-matter physics in 1982 in three leading journals as a function of the number of authors. In universities the groups often consist of a faculty member and a graduate or postdoctoral student; in industrial and government laboratories they are likely to consist of colleagues on the staffs of these institutions or of a staff member and a

20 HIGHLIGHTS, OPPORTUNITIES, AND NEEDS l l 140 120 _ 100 _ =~60 _ 1 40 _ , _ (a) Physicol Review Letters vols. 48, 49 tl982) 1 20 _ 1 2 3 ~ 5 6 7 8 9 10 Number of Authore 600 500 a 40 ~_ o z l l l l l l l l l 350 ~ (c) Solid Stote Communicotions~ vols. 41 - 44 ( 1982) 300 250 200 150 o l . . ) ~ ~ ~ 1 2 3 4 5 6 7 8 9 )10 Number of Authors 700 o O (b) The Physicol Review ~ vols B25-B26 (1982) 300 _ _ 200 _ _ 100 _ ~ 1 2 3 4 5 6 7 8 9 310 Number of Authors FIGURE 1 Histogram of the number of papers in condensed-matter physics published by leading journals in 1982 as a function of the number of authors: (a) Physical Review Letters, (b) The Physical Review, (c) Solid State Communications.

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 21 postdoctoral researcher. It is estimated that there are about 800 such groups throughout the country. This tendency to conduct research in condensed-matter physics individually or in small groups is displayed both by theorists and by experimentalists, even those who do their experimental work at large, national facilities. The individual re- searcher thus forms the backbone of research in condensed-matter physics, and the continued health of this area of physics is inextricably intertwined with the existence of adequate support for that backbone. In what follows we make several recommendations directed toward accomplishing this. In doing so we recognize that a balance must be struck between the needs of researchers in their own laboratories and those of the external, user facilities that provide the equipment not available in individual laboratories. Both are real, both must be met, and there is a cost to each. The fact that research in condensed-matter physics is done primarily in small groups does not make it inexpensive. At the same time, the nature of the research equipment provided to users at the national facilities, and the staff needed to make it usable to visiting researchers, ensures its high cost to build and maintain. Because of large operating costs and the growing fraction of the condensed- matter community that uses them, user-oriented national facilities have the potential of drawing needed resources from the individual researchers in their own laboratories. Both needs must be met over the next decade. This will require the appropriation of enough new monies that the well-being of national facilities for users will not have a negative impact on those researchers who do not use them, and vice versa. Support for Individual Researchers MANPOWER It is vital that there be a continuing stream of new scientists entering condensed-matter physics, to provide fresh ideas and to participate in the research that will keep the discipline lively and to train the students who will eventually replace them. At present there are great opportunities for exciting work to be done in condensed-matter physics. But many physics departments find that there are more graduate students who are eager to pursue these opportunities than can be supported. This situation represents a lost opportunity to progress rapidly with the science as well as a lost opportunity to preserve and augment the nation's scientific and tech- nological manpower in an area with important implications for the electronics industry and national security.

22 H/GHLICHTS, OPPORTUNn/kS. AND NEEDS The national laboratories have performed an important educational role in the postdoctoral training of young researchers as well as the training of graduate students who have carried out their thesis research using laboratory facilities. It is important to maintain the ability of the laboratories to hire postdoctoral fellows. This is extremely difficult in the face of constricted budgets at the laboratories, and provision should be made for the continuation of the postdoctoral program. Moreover, it is essential that there be opportunities for the most talented young investigators to obtain support for their research once they have left graduate school and have elected to pursue careers in a university setting. Otherwise science will decline because students will no longer enter the field. It is also important that senior scientists who leave industrial or government laboratories to assume faculty positions in U.S. universi- ties, as well as those who join our universities from abroad, have opportunities to obtain support for their research. Otherwise our universities will lose these sources of their enrichment. It is equally essential that senior scholars doing first-class research at the frontiers of knowledge continue to have their work supported at adequate levels for the contributions that their work makes to knowl- edge itself. However, as an illustration of recent trends, the Division of Mate- rials Research of the National Science Foundation has found it necessary to decrease the number of grants (by about 20 percent over the past 5 years) to assure the viability of the best research programs through an increase in the average size of each grant awarded. Such a cutback in the size of the funded condensed-matter physics community should not be mistaken for quality control. The latter is provided by the turnover that occurs annually among grantees through the review of the proposals submitted to federal funding agencies. Diversity in the range of research activities shrinks with the reduction in the number of grants. The increasing competition for a decreasing number of grants gives rise to a tendency for investigators to be conservative in the submission of proposals by omitting speculative projects in favor of those that are almost guaranteed to be successful. This is not the way in which major advances in science are made. Despite such efforts to increase the level of funding it is still the case that it is virtually impossible for an active research group to survive if its support comes from a single grant. In order to restore support for those able scientists who have lost funding for this reason, and to provide resources to new scientists entering the field, it is important that there be an increase in the overall

HIGHLIGHTS, OPPORTUNI TIES, AND NEEDS 23 number of grants supporting research in condensed-matter physics. We believe that further cuts in the number of principal investigators currently supported would be inimical to our national interests. At the same time, it is clearly essential to be able to fund new young investigators, as well as to increase the funding of some currently supported young investigators as they develop into the major research directors of the next decade. Consequently, We recommend that over the next 4 years sufficient new monies should be appropriated to provide for an annual increase of at least 3-4 percent in the total number of investigators in condensed-matter physics supported by the several federal funding agencies and for increases in grant sizes. We stress that the purpose of this recommendation is to accelerate scientific progress, to exploit rapidly expanding opportunities, and to ensure continued availability of skilled manpower in a field whose health is essential for maintaining the vital flow of new technology. lNSTRU MENTATION Crucial to an experimentalist's ability to perform experiments at the technical limits of a subject area is having equipment at the state-of- the-art level. Experience has shown that improvements in scientific instrumentation invariably lead to significant new discoveries. With the passage of time, and the steady improvement in the quality of experi- mental equipment commercially available, much of the instrumentation in university laboratories in the United States is no longer state of the art, at the same time that the cost of its replacement and upgrading by state-of-the-art equipment has increased substantially. Recent studies show that the rate of increase in the cost of such equipment has averaged approximately 17 percent per year for the past several years. This is much higher than the rate of inflation of the consumer price index for the same period. The changes in the directions of research in condensed-matter physics in the past few years have brought with them needs for qualitatively new kinds of experimental equipment that were not in existence when the decade began and that are costly. For example, an ultrahigh-vacuum system for research in surface physics may cost in excess of $200,000. The study of the remarkable properties of artificially structured materials, such as semiconductor superlatt~ces' requires having sam- ples of such materials. Specialized equipment is necessary for their preparation, so that the cost of materials preparation in this field is . . . . .

24 HIGHLIGHTS, OPPORTUNITIES. AND NEEDS high. A fully instrumented molecular-beam epitaxy unit can cost $1 million. Few universities have one. This means that university re- searchers are essentially shut out of some exceedingly important areas of research. One of the significant changes that has occurred in the instrumenta- tion needs of experimentalists during this period is their utilization today of powerful computational resources. Once an almost exclusive preserve of theorists, computers now control experiments and perform on-line data analysis. Qualitatively new capabilities have emerged in diverse applications such as on-line Fourier transformation for infrared spectroscopy or studies of chaotic processes, and image simulation for electron diffraction. Some experimentalists require only relatively small microcomputer systems, but these must be available for each experiment in the laboratory. Others require systems with sophisti- cated graphics and the ability to process large data files. Such systems are becoming available for about $50,000. Accompanying the change in the kinds of instrumentation that are being, and will continue to be, used increasingly in condensed-matter research is the fact that in many cases more people are required to operate and maintain this equipment, increasing the cost of that research thereby. In addition to making it possible for research at the highest levels to be conducted in these and other fields in our universities, there is another, educational, aspect to making such equipment available to university laboratories throughout the country. If the products of our graduate programs are to be able to step into positions in universities, industrial laboratories, or government laboratories where such equip- ment is being used and employ it productively, they must be trained in its use while graduate students. This situation of aging instrumentation coupled with a shortage of renewal funds, and the problem it poses for the future of experimental science in the United States has been recognized in studies conducted recently by the National Science Foundation and the Association of American Universities, among others. In response to it, the Division of Materials Research (DMR) of the National Science Foundation (NSF) has established an ongoing instrumentation program that had $4 million budgeted for it in FY 1983 and $7.6 million in FY 1984, of which perhaps 40 percent goes for condensed-matter physics research. At the same time the Department of Defense (DOD) has begun a program to improve research instrumentation at universities, not just in con- densed-matter physics, with $30 million in FY 1983 funds. It is in

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 25 tended that this initiative continue for 5 years, with $30 million budgeted in each fiscal year. The response to these instrumentation programs was overwhelming. Approximately $27 million in requests was received by the DMR for $4 million of FY 1983 funds, while $750 million in requests was received by the DOD for $30 million of FY 1983 funds. Even allowing for the possibility that not all of the requests were of equally high priority, the magnitude of this request indicates the great need to upgrade or replace existing instrumentation in university laboratories. In the face of the magnitude of this need, the DOD and the NSF initiatives, while welcome indeed, are by themselves inadequate to meet it. It is, moreover, a need that must be met now: the longer a massive up- grading of scientific instrumentation is delayed, the larger becomes the degree of obsolescence of equipment in U.S. laboratories and the greater the overall cost of its replacement. Additional funds for this purpose are urgently needed. Consequently, We recommend that sufficient new monies be appropriated to enable federal agencies supporting condensed-matter research to dedicate a certain continuing portion of their support dollars to instrumentation programs. At present levels of support we recommend that this portion be of the order of 20-25 percent. We believe that over the next 4 to 5 years U.S. laboratories will be significantly revitalized thereby. It is important, however, that support for instrumentation be provided on a continuing basis in the future in order that U.S. laboratories remain in the forefront of research. COMPUTATION Almost all areas of this report confirm that computers play a vital and increasing role in condensed-matter physics. Therefore this trend must be recognized by funding agencies and appropriate provision made for the purchase and maintenance of the special computer systems re- quired for research progress. Computers have had an enormous impact on both the speed and the kinds of condensed-matter calculations that can now be done. They have become theoretical laboratories for dynamical simulations of con- densed systems and for their statistical analysis by classical or quantum Monte Carlo methods. Specifically configured computers are now being designed and built to address particular types of theoretical problems. This increased use of computers by theorists is making present-day

26 HIGHLIGHTS, OPPORTUNI TIES, AND NEEDS research in condensed-matter physics more rewarding but also more expensive. A supercomputer, such as the CRAY-XMP, costs around $10 million, and at present only three universities in the United States have one. A computer of the type of a VAX 11-780 costs in the vicinity of $200,000. Even if research groups do not own their own computer, the cost of purchasing computer time can be a significant portion of the cost of present-day research. The future health of the field requires that this clearly identified need for computers be accommodated. As computing needs are diverse requiring both increased capacity and capability they cannot all be filled by the medium-sized main- frame computers found on most research campuses. There is a specific need in theoretical work for advanced computing capabilities. Some of these can often be met by adding a fast processor to a conventional computer at a cost of about $40O,OOO. Almost an order of magnitude or more additional computing power can be provided by modern supercomputers and, in some fraction of cases, the provision of time on such machines if not the machines themselves for condensed- matter research is essential. The future funding patterns must accom- modate the growing demands for computer use. To this end, We recommend that sufficient new monies be appropriated to allow the several federal agencies supporting condensed-matter research to identify a continuing fraction of the total budget to be devoted to the special computing needs of condensed-matter research. The assignment to computing of 10 percent or more of the total present budget would appear well justified. The funds so assigned could be used for the purchase of computer time or for the purchase and maintenance of dedicated equipment. In view of rapid changes in computer technology and patterns of use in the physics community, this fraction should be reconsidered after the next few years of experience. The scientific community and the federal funding agencies should work together to promote more effective use of major computer resources through networking, standardization, and the establishment of user assistance groups. FUNDING The chances of realizing the research opportunities that the coming decade offers will be significantly enhanced by an increase in the number of individuals carrying out this research, an increase in the level of support that they receive, and the provision of the increasingly more sophisticated, and the increasingly more costly, equipment that they will need in their work.

HIGHLIGHTS. OPPORTUNITIES, AND NEEDS 27 The costs of conducting a modern research program include the maintenance of equipment, the operating or running costs, and the salaries and benefits for personnel. These costs will increase more rapidly than inflation because of the increased sophistication of the required equipment and the expected increases in tuition for graduate students. The national investment required for the adequate support of basic research in condensed-matter physics by individual researchers, how- ever, is not great, even though the return on the investment is large. There is heartening evidence in the current federal budget, through its approximately 20 percent increase in support for basic science over the level for last year, that this is recognized. However, more still needs to be done to capitalize on the opportunities that exist. We estimate that implementing the preceding recommendations will require an increase in funding for research in condensed-matter physics at a steady annual expansion rate of approximately 20 percent in constant dollars for an additional 3 years. We strongly recommend that this increase take place. The special claim of condensed-matter physics for research support from federal and industrial sources lies in its record of converting deep science into benign and sophisticated industrial technology on a time scale that is often no more than 5 to 10 years. This process is still vigorously under way with such notable new scientific discoveries as the quantized Hall eject, valence fluctuations, heavy electron-mass metals, electron localization due to disorder, artificially structured materials, conducting polymers, chaotic phenomena in solids and liquids, and solitary wave phenomena in solids. If the resources become available to carry out the research necessary to exploit these new discoveries, the impact An industrial technology will be even greater than what has gone before. Support for National Facilities Some of the national facilities are comparatively new; others have been in existence for many years. Because of their importance for the nation's scientific effort, the facilities that continue to maintain a high level of scientific excellence should be adequately supported. Planning for new facilities to meet the needs of new areas of condensed-matter physics that are now developing must begin in the near future. The needs of the neutron and synchrotron facilities have been subjected to detailed scrutiny recently by several panels sponsored by the NSF and the Department of Energy (DOE). The most recent of

28 HIGHfIGHTS,OPPORTUNITIES,AND NEEDS these studies* was prepared while this report was being written. We will have occasion to refer to it in what follows. NEUTRON FACILITIES The existing high-flux reactors, the cornerstones of the U.S. neu- tron-scatter~ng program, are underfunded and understaffed. Relative to their Western European counterparts they are falling seriously behind in instrumentation. Therefore, We recommend that a concerted and coordinated effort should be undertaken to expand the effectiveness of our high-performance reactors by adding new, diversified instruments along with personnel necessary to design, build, and utilize them in the user mode. We estimate that at least ten new instruments are needed, requiring an increase in annual operating costs of $2 million to $3 million for manpower needed for their design and use. About $20 million to $30 million is required for building such instruments, to be spent over 5 to 7 years. Instrumentation plans beyond the level projected above may be warranted but should be justified by demonstrated user needs. Note that this estimate does not attempt to address the somewhat different needs of the chemistry and biology communities. A 1984 Panel on Neutron Scattering, considering the total scientific commu- nity, estimated a need for ~30 new instruments." Spallation sources provide new opportunities to expand the power of the neutron as a probe of condensed matter. The United States currently has two pulsed spallation sources. The Los Alamos Neutron Scattering Center (LANSCE) facility at the Los Alamo s National Laboratory is compromised currently by the pulse structure of the LAMPF proton beam that supplies it. This situation will be corrected by the addition of a proton storage ring (PSR) scheduled for completion in 1986. It is also restricted by the small experimental hall. The Intense Pulsed Neutron Source (IPNS) at the Argonne National Laboratory, with an active otltside-user community, an experienced stab, and an adequate experimental hall, is the highest-performance source in operation at present. * Major Facilities for Materials Research and Related Disciplines (National Academy Press, Washington, D.C., 1984). This will be referred to below as the report of the Seitz-Eastman committee. ~ Current Status of Neutron-Scattering Research and Facilities in the United States (National Academy Press, Washington, D.C., 1984).

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 29 We therefore recommend that funds be appropriated to enlarge the LANSCE instrument hall (a $15 million construction project has been proposed) and operation of IPNS be continued until the latter's ongoing activities can be accommodated by a more powerful and cost-effective LANSCE, provided this can be budgeted without jeopardizing the necessary rejuvenation of the high-performance reactors. Very recently Argonne has proposed the upgrade of IPNS by the replacement of the existing accelerator with one of new design (fixed field, alternating gradient) with a sevenfold increase in proton current. If this design is shown to be practical and cost-effective relative to LANSCE, it will be necessary to reconsider our spallation-source priorities in the light of the existing investments. There are no comprehensive plans at present concerning the status of our neutron capabilities for the 1990s. Given the uncertainties in the lifetimes of existing facilities and the time necessary for the design and construction of new facilities, it seems advisable for the neutron- scattering community to initiate discussions immediately leading to such a plan. The feasibility and desirability of both steady-state and pulsed sources should be studied. The possibility of establishing such a facility through international cooperation should also be fully ex- plored. We therefore recommend that supplemental funds be made available to interested qualified institutions to investigate various options for an advanced neutron source. These studies should be done in parallel and in consultation with a panel of outside users charged with devising a plan that will ensure that our neutron-scattering needs will be met in the l990s and beyond. SYNCHROTRON RADIATION SOURCES RECOMMENDATIONS Synchrotron radiation has had a broad impact on studies of both the structural and electronic properties of condensed matter. This is due to its unique high brightness, wide tunability, high polarization, and narrow angular divergence (and, in some instances, time structure). These properties are similar to those of laser sources, but the wave- length range of synchrotron radiation extends from that of the shortest known laser wavelength throughout the ultraviolet, soft-x-ray, and hard-x-ray regions. It is recommended that the current new generation of synchrotron facilities be completed as soon as possible since their high brightness will serve the short-term needs of the next 3 to 5 years.

30 HIGHLIGHTS, OPPORTUNITIES, AND NEEDS The main scientific emphasis of these short-term objectives should be in the following areas: (i) Current beam-line instrumentation should be refined in order to achieve higher resolution of photon monochromators in the conventional VUV (0-100 eV) and x-ray (4-15 keV) ranges. This will allow new types of studies to be made of electronic and structural phenomena in conventional solids as well as in low-dimensional sys- tems such as surfaces, polymers, and liquid crystals. (ii) Novel new instrumentation should be developed for soft x rays in the 100-4000 eV range that uses combinations of conventional diffraction-grating tech- nology with new synthetic materials such as multilayer mirrors and other x-ray optical elements. This would allow high-resolution studies of the shallow core-level spectra of all elements. In addition both extended-x-ray absorption fine-structure (EXAFS) and high-resolution near-edge studies could be performed using K or L edges of elements with an atomic number smaller than that of xenon. In order to exploit the potential of insertion devices in the x-ray region it is important that the design allow first harmonic undulator radiation at energies up to ~20 keV. A commitment should begin immediately toward the next generation of high-brightness synchrotron facilities using insertion devices. This should be a two-step approach. New undulator and wiggler devices should be constructed on existing stor- age rings so that insertion-device technology will move ahead rapidly and be ready for possible new rings. New optical devices should be developed to match insertion device sources; this should be done in parallel with the development of new sources, since higher resolution and wider tunability cannot be achieved simply by attachment of existing beam lines to new sources. As a second priority, planning should begin immediately leading to proposals for a next-generation, possibly all-insertion device machine. Ideally, this machine should be completed in the early l990s, since projected user demand will saturate then-existing facilities by that time. The design parameters, such as electron energy and physical size, should be determined by scientific considerations, but the three areas of spectroscopy, scattering, and micros- copy should be accommodated. The 6-GeV machine recommended by the Seitz-Eastman committee appears to meet these needs. The overall costs of such a next-generation synchrotron source are in the range of $160 million, and construction could take place over a period of 6-7 years. Firm decisions on when to build such a machine should be made on the basis of new scientific opportunities, user demand, and ongoing experience with the undulator and wiggler facilities discussed above.

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 31 HIGH-MAGNETIC-FIELD FACILITIES RECOMMENDATIONS Laboratories for the production of high magnetic fields (>15 T. where 1 T_ 104 Oe) and their utilization in condensed-matter research exist in France, Holland, Belgium, Japan, Poland, the Soviet Union, and the United States. The National Magnet Laboratory at the Massachusetts Institute of Technology is the only major user facility for high-field research in the United States. A wide variety of steady- field magnets exist there and are categorized by their peak fields, bore sizes, and homogeneity. The largest field currently available there is 29 T. in a 3.3-cm-bore hybrid configuration. Magnetic fields above 30 T are economically feasible only in pulsed operation. Nondestructive, repetitive pulsed fields in the range 40 T c H c 60 T are now available in Holland, Japan, and the Soviet Union. A 75-T configuration will soon be operating in Osaka, Japan. A high-magnetic-field facility has just been completed at the Institute for Solid State Physics (ISSP) in Tokyo, Japan, at a cost of about $10 million. It can produce a variety of nondestructive pulsed fields (c50 T); it can produce fields of 50-100 T by plasma compression that may be nondestructive; and it can produce a 100-500 T implosion-generated field that is totally destructive of the sample. The ISSP group has been generating fields of 100 T for several years, which have been used in studies of cyclotron resonance and various other phenomena in semi- conductors. No comparable facilities are available in the United States, although much of the seminal technology was developed in this country. The availability of high magnetic fields has yielded such experimen- tal results as the discovery of the fractionally quantized Hall effect. More generally, high-field magnets expand the phase diagram of a solid by adding a new variable, the magnetic field, to the usual variables, pressure and temperature, thereby increasing our knowledge of prop- erties of solids under extreme conditions. For these reasons, and the paucity of high-field magnets in the United States, We recommend that new money should be made available to enable greater emphasis to be placed on the generation of pulsed high magnetic fields at the National Magnet Laboratory and/or at a new site elsewhere in the United States. The cost of duplicating the high-magnetic-field facility in Osaka is estimated to be $1 million to $2 million. ELECTRON-MICROSCOPE FACILITIES RECOMMENDATIONS The country's electron-microscope facilities provide a reservoir of talent and expertise necessary to generate the innovative instrumenta

32 HIGHLIGHTS, OPPORTUNITIES, AND NEEDS lion crucial for promoting the growth of the power and subtlety of electron-microscopic investigations in the coming decade. There ap- pear to be four major areas in which advanced instrumental initiatives could have a major impact on the development of the field during this period: (1) development of ultrahigh-vacuum sample environments for surface studies; (2) development of efficient instrumental accessories for microanalytical techniques such as electron energy loss spectros- copy; (3) development of low-temperature specimen stages and spec- imen preparation techniques necessary for systematically attacking questions about the structures of large biological molecules and of many others that are of interest to condensed-matter physics; and (4) development of computerized data collection and analysis. It is esti- mated that the cost of the major capital equipment required for im- plementing these instrumental initiatives would average $1 million for each, spread out over a period of 2 years, for a total of $4 million. The increase in the operating budgets of the institutions participating in these initiatives is estimated to be $4 million, to be achieved over a period of 3-4 years. Our recommendation in this area is as follows: Advanced instrumentation initiatives in the four areas of electron microscopy cited above should be established in response to competitive proposals from interested institutions. If necessary, the federal funding agencies should stimulate the submission of such proposals. GENERAL RECOMMENDATIONS CONCERNING NATIONAL FACILITIES There are two broad categories of users of national facilities. Committed users are those whose research programs are built nearly exclusively around the use of these facilities and include the scientific staff of the facilities. By contrast, occasional users have research programs based on other techniques, usually at their home laborato- ries, but whose research is increased in scope by the power of these other specialized techniques. The long-term vitality and future growth of national facilities depend crucially on a broad base of these occasional users who have neither the time nor the financial resources to become expert in these techniques but who furnish nonetheless a wealth of novel materials and ideas for experiments. In order to aid the integration of these occasional users into the activities of the facilities, We recommend that special funding be set aside for the purpose of accommo- dating occasional users at the national facilities. This money would help finance travel and living expenses, particularly for university users, and

HIGHLIGHTS, OPPORTUNITIES, AND NEEDS 33 provide an increase in the in-house support staff. This program should be formulated by the individual facilities in consultation with university and industrial collaborators and funded on the basis of separate proposals from these facilities. We estimate that a significant trial program would require $4 million to $6 million per year over a 3-4 year period. Recently established national facilities (e.g., those dedicated to research employing synchrotron radiation or high-resolution electron microscopes) have been developed as user facilities or as DOE Centers for Collaborative Research. The independent peer review of the experiments approved to be done improves the quality and nature of the research at these facilities. At the same time, the ability to respond to rapidly emerging scientific opportunities and the timely development of new experimental techniques requires that a certain fraction (per- haps 30 percent) of the available time be allocated at the discretion of the in-house staff. Therefore, We recommend that in the future it is desirable that national facilities should operate in the user mode in which the majority of experimental time is allocated by independent peer review. There are at least two modes in which this peer review may operate: review of experiment-by-experiment proposals by occasional users and peer review of proposals for participating research teams (PRTs) that undertake to construct, maintain, and carry out research programs using instruments on a shared basis with non-PRT members. Finally, it is our strongly held view that the needs of the individual researcher, which have been outlined above in the section on Support for Individual Researchers, are so great at this time that the highest priority for the use of new monies for the support of condensed-matter physics is in meeting those needs and for the upgrading of the existing national facilities that is necessary for the achievement of their full potential. When this has been accomplished, the construction of the new national facilities should begin. University-Industry-Government Relations One of the primary strengths of condensed-matter physics is that forefront research of the highest quality is carried out at industrial laboratories as well as at universities and government laboratories. This is due to the fact that condensed-matter physics is closest to applications in technology of all the subfields of physics. It argues for a strong coupling between universities and national laboratories, where

34 HIGHLIGHTS, OPPORTUNI TIES, AND NEEDS most of the basic research in condensed-matter physics is done? and industry, where the results of that research, as well as of the research done in-house, is transferred into technology. industry also benefits greatly from the pool of condensed-matter physicists produced each year by this country's universities and from those trained in postdoc- toral programs at national laboratories. For their part, universities have received support from industry in the form of grants of equipment, funding for research projects, and support for graduate students. How- ever, if the strongest possible coupling between universities, govern- ment laboratories, and industry is to be achieved, the support of university and laboratory research by industry should go well beyond the mere provision offunds and equipment: research cooperation is also required. At the same time, continuing efforts should be made to in- crease the research cooperation between the national laboratories and university scientists, since special facilities exist at the national laboratories that are not available elsewhere. The realization of such cooperation will require the coordinated efforts of universities and industry, and of the federal government as well. The following recom- mendations outline our views of the roles of each of these partners in this process. 1. What government should do: Establish policies, including tax incentives, to stimulate fundamental research in industry. Provide support for students engaged in cooperative university- industry research. Encourage and facilitate the flow of scientists between federal labora- tories and universities for cooperative research programs. Maximize access by outside users to the special facilities available only at the federal laboratories. 2. What industry should do: Increase the amount of in-house research even beyond the levels directly supported by the policies suggested in point 1 above, i.e., through the use of corporate funds. Establish and fund programs that enable industrial scientists to take sabbatical leaves in universities and at national laboratories. Receive university faculty and laboratory researchers in industrial laboratories for sabbatical leaves and summers. Provide direct support of faculty and departmental research grants (e.g., the IBM programs). Provide direct support of graduate and postdoctoral fellowships (e.g., the IBM fellowship program).

HIGHLIGHTS. OPPORTUNITIES. A ND NEEDS 35 Formulate cooperative research projects with graduate students (e.g., the MIT-AT&T Bell Laboratories program). Provide instrumentation for special facilities at national laboratories. 3. What universities should do: Implement cooperative research and support programs with indus- try, as MIT has done in materials processing. Adopt a limited form of the "Japanese model" in which applied physics research in high-technology areas, such as semiconducting lasers, photonics, and electronics is supported by industrial firms directly involved in the manufacture of materials, devices, compo- nents, and systems employing these technologies. Cooperate in the graduate training of industrial employees engaged in applied research. Arrange for sabbatical leave for federal laboratory researchers in university departments. This support can take the form of direct research contracts; the gift or loan of equipment, devices, and components; and the support of graduate students.

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