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Condensed-Matter and Materials Physics: The Science of the World Around Us 1 Overview In the past decade, the field of condensed-matter and materials physics (CMMP) has enlarged its scope enormously, embracing a far wider range of problems than ever before. At the heart of CMMP is the quest to understand, through a combination of experimental, theoretical, and computational investigations, how unexpected phenomena emerge when large numbers of constituents interact with one another. These constituents, traditionally electrons, atoms, and molecules, have now been extended to a vast array, including complex biological molecules, nanoparticles, cells, and even grains of sand. In addition, researchers are now applying CMMP approaches and techniques to interacting systems of constituents such as Internet nodes, economic transactions, and entire organisms. This tremendous range of constituents leads to a spectacular diversity of emergent phenomena. By understanding these phenomena, CMMP researchers affect people’s lives in countless ways, from improving our understanding of nature to developing new technologies. Historically reliable drivers for the discovery of new emergent phenomena are new materials and devices. Examples of materials and phenomena first targeted by CMMP researchers can be found almost everywhere: semiconductor lasers are in DVD players, advanced magnetic materials store data on computer hard drives, liquid-crystal displays show us photographs and telephone numbers. But these technological marvels tell only half the story. Studies of new materials and phenomena have also led to significant advances in our understanding of the physical world. For example, the development of ultrapure layered semiconductors made possible not only the production of high-speed transistors for cellular telephones
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Condensed-Matter and Materials Physics: The Science of the World Around Us but also the discovery of completely unexpected new states of matter, such as the fractional quantum Hall state. Efforts to understand magnets, ferroelectrics, superconductors, polymers, and liquid crystals, exploited in innumerable applications, spurred the development of the elegant, unified conceptual framework of broken symmetry that not only explains how the characteristic behaviors of these materials are related, but also underlies much of modern physics. The pure and applied aspects of condensed-matter and materials physics are opposite sides of the same coin that define and enrich the CMMP field. SIX SCIENTIFIC CHALLENGES FOR THE NEXT DECADE One of the main findings of this report is the identification of six grand challenge areas in which CMMP research is poised to have a large and enduring impact in the next decade. These research areas reflect both fundamental intellectual challenges and societal challenges, in keeping with the dual pure and applied nature inherent to CMMP. While CMMP has been developing many of the needed key tools and is central to many of these challenge areas, all of them will require the combined efforts of researchers from many disciplines in order to succeed. The broad spectrum of research covered by CMMP includes many important problems outside those identified in this report, and areas currently unforeseen are certain to arise from discoveries in the next decade. Nonetheless, the challenges identified here capture much of the intellectual vitality and range of the field as it moves into the next decade. These scientific challenges, discussed in turn below, are as follows: How do complex phenomena emerge from simple ingredients? How will the energy demands of future generations be met? What is the physics of life? What happens far from equilibrium and why? What new discoveries await us in the nanoworld? How will the information technology revolution be extended? How Do Complex Phenomena Emerge from Simple Ingredients? The notably successful “reductionist” approach to physics focuses on the laws that govern the motion of ever-smaller fundamental constituents of matter. Indeed, in principle, all of CMMP, not to mention chemistry and biology, is believed to follow from the solution of one simple equation, the Schrödinger equation, governing the quantum dynamics of electrons and ions. Conversely, “emergence” refers to the fact that the behavior of large, complicated systems made of many diverse building blocks is often distinct from, and even relatively insensitive to, the detailed properties of the individual constituents. Reductionism stresses the understanding
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Condensed-Matter and Materials Physics: The Science of the World Around Us that comes from studying systems at a more and more microscopic level, while emergence finds conceptual clarity in the collective behavior of large systems. A vivid example of emergence is the brain that you are using to read and understand this page. A human brain consists of roughly 100 billion neurons. Those neurons, which in one of the most notable advances of modern biology are now reasonably well understood individually, in some sense represent the building blocks of your consciousness. Yet no one would claim to understand how this most fascinating of all natural phenomena emerges from the behavior of the individual neuron. As a simpler example, metals exhibit very similar macroscopic properties, despite the fact that they might be made of copper atoms, or silver atoms, or even complicated organic molecules. CMMP, more than any other scientific discipline, seeks to understand at a quantitative level the connection between the microscopic and the macroscopic in systems with many interacting constituents. Although all material systems consist, ultimately, of the same well-understood electrons, protons, and neutrons, their aggregate behaviors are stunningly diverse and often deeply mysterious. Superconductivity, the dramatic vanishing of all electrical resistance of certain materials below a critical temperature, is one of the best-known examples of emergence. In studying superconductivity, the goal is both to characterize the amazing macroscopic quantum behaviors of the superconducting state and to understand what aspects of their microscopic structure cause certain metals to become superconductors and other metals not to. The discovery, understanding, and application of emergent phenomena are the core activities of CMMP. New materials inevitably exhibit new and often unanticipated behaviors. Existing materials, pushed to new regimes of high purity, low or high temperatures, high pressures, or high magnetic fields, have always yielded surprises, including wholly new phases of matter. Fresh theoretical perspectives frequently bring into focus hitherto perplexing or ignored features of existing observations that reflect previously overlooked organizing principles and suggest new avenues for further experimental inquiry. The ever-increasing precision with which the properties of materials can be measured permits new ideas concerning the underlying microscopic origins of emergent behaviors to be tested with unprecedented rigor. Emergent phenomena are not merely academic curiosities; many result in technological advances of immense societal importance. The discovery of superconductivity in 1911 ultimately enabled, decades later, magnetic resonance imaging and thereby revolutionized modern medicine (see Figure 1.1). Liquid crystalline materials, in which large numbers of asymmetric molecules in solution exhibit a dizzying variety of emergent phases, are used in everyday electronics like cell phones and laptop computers. The diversity of emergent phenomena ensures the beauty, excitement, and deep
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Condensed-Matter and Materials Physics: The Science of the World Around Us FIGURE 1.1 The emergent phenomenon of superconductivity plays a key role in magnetic resonance imaging (MRI), a technique that has revolutionized medicine. (Left) Modern high-field clinical MRI scanner. (Right) MRI scan of the brain. SOURCES: (Left) Photograph courtesy of Kasuga Huang. (Right) Image courtesy of Jon Dattorro, Stanford University. practical utility of condensed-matter and materials physics as an inexhaustible resource. The challenge is to understand how such collective phenomena emerge, to discover new ones, and to determine which microscopic details are unimportant and which are essential. How Will the Energy Demands of Future Generations Be Met? The availability of affordable and renewable energy sources represents one of the biggest challenges that will face humankind in the 21st century. The United States must develop affordable, renewable energy sources to reduce dependence on fossil fuels while minimizing carbon emissions and other sources of harm to the environment. Promising technologies for solar energy, hydrogen fuel cells, solid-state lighting, rechargeable batteries, and improved nuclear power will all play critical roles, but fundamentally new scientific approaches are also needed to address the magnitude of this challenge and its urgency effectively. CMMP is uniquely positioned to address these challenges, which require a better understanding of energy conversion and storage as well as the creation of new technologies for increasing end-use energy efficiency. Basic scientific discoveries in these areas will provide the underpinnings for the creation of new advanced energy technologies. How can sunlight be converted to usable energy more efficiently? In what new ways can hydrogen be generated and stored? Can renewable, affordable, and benign fuels be developed? How can
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Condensed-Matter and Materials Physics: The Science of the World Around Us new approaches and new materials be used to create better light-emitting diodes and light conversion materials (see Figure 1.2)? Can new materials be developed to operate under extreme conditions, such as those found in nuclear and plasma fusion reactors and in receptacles for waste storage? Discovering and understanding new materials, especially nanostructured materials with novel materials properties, will be key to advancing the energy research frontiers. For example, new superconductors could dramatically reduce energy losses in power transmission, while new thermoelectric materials could enable the drawing of power from waste heat or geothermal energy. No single strategy will provide all the answers, and some approaches may take decades to come to fruition, so research investment over a broad front is needed to meet this immense challenge. What is certainly clear, however, is that new materials, nanoscience, and new theoretical approaches will play a critical role in overcoming many of the technical barriers to achieving energy security. FIGURE 1.2 Comparison of the improvements in the luminous efficacy (lumens per watt) of light-emitting diodes (LEDs) with other lighting technologies (shown along the y-axis) since 1960, indicating the reality for this technology in future lighting applications. The theoretical maximum efficacy of white LEDs is about 300 lumens per watt. LED lighting has the potential to reduce overall electricity consumption in the United States by about 13 percent over the next 20 years. SOURCE: Lumileds Lighting.
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Condensed-Matter and Materials Physics: The Science of the World Around Us What Is the Physics of Life? The phenomena of life offer some of the most profound challenges facing the physics community. How is it possible for functional behavior, recognized as characteristic of living systems, to emerge from inanimate matter? In the past decade, this grand but somewhat amorphous question has been sharpened into the appreciation of the physics problems that arise in thinking about specific biological systems. From bacteria to brains, from picosecond events in single molecules to evolutionary changes over millions of years, physicists are asking new questions about biological systems and providing new ways of studying them. New combinations of experimental techniques from physics and biology have uncovered a previously unimagined layer of richness and precision in the function of biological systems (see Figure 1.3). At the same time, theoretical approaches from physics have predicted new phenomena, provided solutions to classical puzzles, and generated new frameworks for the ever-expanding body of experimental data. With careful nurturing, the coming decade will see the continued emergence of biological physics as a branch of physics. One of the central physics problems that organisms have to solve in order to survive is the problem of reliability in the presence of noise. This problem exists at many different levels of biological organization, from single molecules, to networks of molecules in single cells, to interactions among cells in complex organisms such as humans. Fundamental physical noise sources, such as the random motion of individual molecules and the random arrival of photons at the retina on a dark night, all have measurable effects on the function of biological systems. In some cases these random events provide a limit to the precision with which organisms can carry out their functions, while in other cases living systems exploit fluctuations to find their way more efficiently to a desirable state. New experimental methods are giving a direct image of these random events, sometimes literally. Theorists are trying to understand the strategies that organisms use to suppress or exploit different noise sources, and the next generation of experiments will test these ideas in their natural context. On the one hand, life is a phenomenon of extraordinary precision and intricacy, while on the other hand crucial mechanisms operate in a regime where noise is not negligible. The coming decade will bring a new understanding of this sometimes paradoxical interplay between functionality and randomness. Physicists strive to situate the particular in terms of the general, and nowhere is this more apparent than in CMMP. Materials display a large diversity of behaviors, but over decades the CMMP community has struggled to classify these behaviors and to have general theories within which the behaviors of individual materials can be seen as examples. An important development in the physicists’ attempts to understand the phenomena of life thus is the attempt to see biological phenomena as examples of a wider range of possible phenomena. Again, this idea cuts across
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Condensed-Matter and Materials Physics: The Science of the World Around Us FIGURE 1.3 New questions and new methods for exploring the physics of life. (a) Optical trapping makes it possible to observe the “reading” of the genetic code by a single molecule of ribonucleic acid polymerase (RNAP), monitoring the steps from one base pair to the next along deoxyribonucleic acid (DNA). (b) Genetic engineering and fluorescence microscopy are combined to observe the intrinsic noise as cells regulate the expression of individual genes; here molecular noise is translated in changes in color. (c) Second harmonic generation from molecules dissolved in the cell membrane makes visible the dynamics of voltage changes in the submicron spine structures in the brain where cells make contact and change their properties as people learn. SOURCES: (a) E.A. Abbondanzieri, W.J. Greenleaf, J.W. Shaevitz, R. Landick, and S.M. Block, “Direct Observation of Base-Pair Stepping by RNA Polymerase,” Nature 438, 460-465 (2005). (b) M.B. Elowitz, A.J. Levine, E.D. Siggia, and P.S. Swain, “Stochastic Gene Expression in a Single Cell,” Science 297, 1183-1186 (2002). Reprinted with permission from the American Association for the Advancement of Science. (c) G.J. Stuart and L.M. Palmer, Pflugers Archiv 453, 403 (2006). many levels of biological organization. Progress is being made on understanding what makes proteins, essential molecular building blocks of life, special in the broad class of heteropolymers. Similarly, principles are being suggested that might single out what is unique about the networks of biochemical interactions in a cell as opposed to an arbitrary network. For many years physicists and biologists both have been interested in the way that molecular mechanisms of learning in the brain sculpt the dynamics of neural networks to perform particular functions, in effect selecting particular networks out of all possible ones. In the past decade, all of these problems have come into sharper focus through a combination of theory
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Condensed-Matter and Materials Physics: The Science of the World Around Us and experiment, often in vigorous collaboration. The essential tension is between the “fine tuning” of each mechanism for its particular function and the evident robustness of these functions to many variations, both in the life of one organism and over evolutionary history. The coming decade will see both practical and conceptual progress on this broad class of problems, shaping our view of how the many components of each biological system interact to achieve the functions recognized as life. The study of biological systems has traditionally been organized around particular organisms and subsystems. Dramatic developments in biology itself have made it possible to break down some of these boundaries, so that the tools which allow researchers to explore the genetics of bacteria also can be used to explore the way in which neurons in the human brain acquire their identity and function. Physicists have gone farther, asking conceptual questions, such as those about noise and robustness described above, which cut across the classical layers of biological organization. While it remains to be seen if the physicists’ questions will lead, as hoped, to a genuinely unified theoretical framework—in the same way that CMMP provides a theoretical framework for other macroscopic phenomena—the asking of these new questions has been remarkably productive and has had an impact on both the physics and biology communities. The challenge here is nothing less than to develop further a new branch of science that combines the theoretical depth and quantitative precision of physics with the beautiful and intricate phenomena of modern biology. These developments will have a profound influence on how people think about the world, on how they solve practical problems of human health, and on how they view themselves. What Happens Far from Equilibrium and Why? Many of the most striking features of the world around us are far-from-equilibrium phenomena. The energy that continually strikes Earth from the Sun gives rise to far-from-equilibrium behavior ranging from chaotic weather patterns to the staggering diversity of life. If solar energy were no longer supplied, many systems on Earth would revert to the unchanging state that characterizes equilibrium. Much is understood about systems at equilibrium and near equilibrium, where systems respond as they do to naturally occurring fluctuations in the equilibrium state. However, scientists are just beginning to uncover some of the basic principles that govern a myriad of far-from-equilibrium phenomena, ranging from the molecular processes on the nanoscale that form the basis of life to the clustering of matter within the universe as a whole. Far-from-equilibrium behavior is ubiquitous. It arises across the entire spectrum of condensed-matter and materials physics in a host of problems of fundamental interest and is intimately connected to cutting-edge materials processing.
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Condensed-Matter and Materials Physics: The Science of the World Around Us Far-from-equilibrium behavior both benefits and plagues us in technology and in everyday life. Indeed, some of the most scientifically intriguing outcomes of behavior far from equilibrium emerge in situations familiar in everyday experience. For example, we can see turbulence in cloud patterns as well as in a bathtub; we take advantage of glassy behavior in nearly all plastics but suffer from it in traffic jams; we exploit the breaking up of a stream of fluid into droplets with fuel injection and ink-jet printing but also find it in every leaky faucet. The reach of far-from-equilibrium phenomena extends even farther, to many systems of profound societal importance. In the past decade, CMMP researchers have begun to tackle far-from-equilibrium behavior governing the workings of systems of critical national importance, including the economy, ecosystems, and the environment. As a result, breakthroughs in the area have potential for far-reaching impact across many scientific disciplines. The microscopic origin of collective far-from-equilibrium behavior still remains largely uncharted territory. Most knowledge about how microscopic properties affect the ways in which systems with many constituent particles behave and evolve is based on a powerful formalism—statistical mechanics. However, this framework applies only to situations near equilibrium, in which a system is thermally and mechanically in balance with its surroundings, and thus it covers only a small subset of the phenomena observed around us and confronted in applications. Within the past decade, CMMP research has set the stage for fresh approaches to long-standing problems concerning far-from-equilibrium behavior. Granular matter (Figure 1.4) has been established as a key prototype for a class of systems that exist far from equilibrium because they are trapped in configurations that structurally resemble a liquid (they are dense and highly disordered), but are unable to flow and thus they behave as solids. Systems of this type have prompted the introduction of the unifying paradigm of “jamming,” which suggests that common physics underlies systems ranging from granular matter to the toughest plastics, strongest metallic alloys, concrete, paints, and foam. Ideas have flowered to describe the far-from-equilibrium aspects of living systems, ranging from mechanisms of transport within cells to the organizing principle of robustness, which suggests that living systems have been designed, through evolution and natural selection, to be robust to perturbations. This organizing principle has been connected with ideas from engineering to be applied as a mechanism of state selection in interacting networks ranging from transportation systems to the Internet to the human immune system. These examples illustrate that CMMP researchers are tackling ever-bigger and -broader problems in far-from-equilibrium phenomena. This expansion drives critical needs. Currently, research on far-from-equilibrium phenomena is fragmented into small subfields. These are typically divided along the types of materials
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Condensed-Matter and Materials Physics: The Science of the World Around Us FIGURE 1.4 Granular materials consist of individual solid grains interacting only at contact, yet large assemblies of such grains exhibit a rich set of complex behaviors. (Left) Ripples in a sand dune. (Right) While fluids mix when stirred, granular materials size-separate; this magnetic resonance image of the interior of a layered granular system shows the upward motion of a large particle (dotted circle) in a bed of smaller ones. SOURCES: (Left) Photo courtesy of http://philip.greenspun.com. (Right) Matthias Möbius and Heinrich Jaeger, University of Chicago. or specific phenomena studied—for example, fracture in solids or turbulence in fluids. The field of far-from-equilibrium physics is vast, and it is unlikely that any one organizing principle will work for all far-from-equilibrium systems. Nonetheless, there is great value in identifying classes of systems that might have common underlying physics or that might be tackled by common methods. There have been few incentives to adopt such broader approaches. Despite this, CMMP researchers are finding important connections to a wide range of other fields, both within and outside physics. Over the next decade, it will be critical to find ways to stimulate new links and to nurture crosscutting approaches in order to realize the vast potential of this research.
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Condensed-Matter and Materials Physics: The Science of the World Around Us What New Discoveries Await Us in the Nanoworld? Nanoscale materials straddle the border between the molecular and the macroscopic. They are small enough to exhibit characteristics reminiscent of molecules but large enough for their properties to be designed and controlled to meet human needs. The first human nanotechnology, the integrated circuit (Figure 1.5), gave birth to the information age. The goal of nanoscience is to plant the seeds needed to grow even more nanotechnologies, ones capable of manipulating matter, energy, FIGURE 1.5 The first human nanotechnology—the modern integrated circuit (a), constructed from billions of individual transistors, such as the one shown (b). An example of nature’s nanotechnology— a field of sunflowers (c), constructed from nanoscale building blocks like deoxyribonucleic acid (DNA) (d). SOURCES: (a) Intel Corporation. (b) Texas Instruments. (c) Bruce Fritz, Agricultural Research Service, U.S. Department of Agriculture. (d) Joseph W. Lauher, State University of New York at Stony Brook.
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Condensed-Matter and Materials Physics: The Science of the World Around Us can carry the “smaller, faster, cheaper” banner of information technology in coming decades. The answer to this question is of strategic economic interest to the United States. To maintain the flow of new products and services, the economic growth, and the dynamism of the industry, new devices to store, process, and communicate information will be needed—devices that can eventually be shrunk to the scale of molecules and atoms. Figure 1.6 illustrates how far information technology has come and how far it can go in the future. What will replace the silicon transistor? What new materials and phenomena will be incorporated into the logic gates of the future? CMMP researchers have ideas, but not answers. There are many physically promising approaches, and each approach presents deep intellectual challenges. The new approaches go by names such as spintronics, plasmonics, and molecular electronics. The possibility of communicating information via spin currents or subwavelength pulses of light, instead of traditional electrical charge currents, opens new vistas for research. And there is the grand quest to harness individual quantum states for computation—quantum computing—with the promise of exponentially accelerated computational speed and potentially unbreakable encryption schemes. As experimentalists study model systems such as Josephson junction-based quantum bits (qubits), theorists are developing new conceptual models such as topological quantum computing. The future looks exciting, and the FIGURE 1.6 The past, present, and future of information technology, from Babbage’s mechanical computer, to the silicon era, to perhaps atomic- and molecular-level systems in the future. SOURCES: Courtesy of Artur Ekert, University of Cambridge, and Tim Spiller, Hewlett-Packard Laboratories, Bristol, United Kingdom.
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Condensed-Matter and Materials Physics: The Science of the World Around Us stakes are high. CMMP researchers can play a key role in extending the information technology revolution, but the CMMP community must be prepared to lower the barriers between basic and applied research and between experiment and theory. The entire scientific and technological community has a unique opportunity to join together to meet this grand challenge. SOCIETAL AND SCIENTIFIC IMPACT OF CMMP RESEARCH CMMP is remarkable for the breadth and depth of its impact on society as well as on other scientific disciplines. While CMMP research formed the cornerstone of the electronics revolution of the 20th century, it is now poised to make vital contributions to addressing problems of the 21st century, such as the global renewable energy challenge and the revolution occurring in the biomedical health care arena. Along with the six scientific challenges for CMMP that are identified here and discussed in greater detail in Chapters 2 through 7 of this report, the challenge to educate the next generation of scientists and citizens is given equal importance by the Committee on CMMP 2010, although the nature of the challenge is admittedly different in character. Further refinement of this challenge identified three key issues: how to educate the next generation of CMMP researchers, how to attract talented people to the field, and how to increase the scientific literacy of the general public and school-age children. Limited public awareness and understanding of science are an increasing danger to U.S. economic security. The CMMP community must now extend educational efforts not only to improve the scientific literacy of the public at large and of the student populations at all levels, but also to increase the pool of students interested in in-depth study of science and engineering. It is critical to infuse a new generation of scientists with the knowledge, skills, creativity, versatility, and sense of wonder needed to meet the challenges to society in the 21st century. The next generation of CMMP scientists should therefore be exposed to many opportunities for hands-on research experience—for example, through undergraduate research involvement—to stimulate interest and excitement in recent discoveries in CMMP, and they should be exposed to a more interdisciplinary educational experience to allow them to work at the newly emerging research frontiers of science and to utilize CMMP research for societal benefit. CMMP is responsible for technological innovations that are leading contributors to national economic development and that enhance the quality of life. The electronics industry today is about a $1.5 trillion industry worldwide, based principally on technology arising from CMMP research, some done more than 50 years ago. This CMMP research has been recognized by Nobel Prizes and many other accolades. Most economically developed regions of the world have large and growing efforts in research over a broad range of scientific fields, including
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Condensed-Matter and Materials Physics: The Science of the World Around Us CMMP, with the belief that this effort will enhance economic growth. For continued growth in the world’s economy, research in the fundamental aspects of CMMP, both experimental and theoretical, is considered by the committee to be essential. It is therefore important to the future of the United States to maintain a leadership position in this basic research field. The energy challenge is an area of great societal concern in which the CMMP community has an exciting opportunity to make major contributions based on the developments of new materials, new systems, and advanced computation and modeling. To succeed in making the transition to renewable energy sources within the first half of the century, a broad research investment strategy is required, based on multiple energy technologies. In addition, given that the energy challenge is clearly a global problem, basic energy-related research also presents an exciting opportunity for international collaboration on basic science and on the new technologies emanating from this research. Condensed-matter and materials physics has a long history of seeding not only developments in fundamental biology, such as the use of x-ray diffraction to study biological structure, but also developments in the practice of medicine. The past decade has been rich with examples in which CMMP has had major societal impact, from the widespread adoption of reliable home pregnancy tests based on gold nanoparticles, to routine magnetic resonance imaging using ever-improving superconducting magnets, to using nanoparticle-based contrast enhancement to image everything from tumors to brain function, to the development of new materials for the increased lifespan of surgical implants. It is expected that CMMP researchers will continue to develop tools that revolutionize the biological and medical fields. CMMP also plays a vital role in other disciplines of science, in two ways. First, CMMP technologies such as materials and devices, ranging from nonlinear organic materials to charge-coupled-device detectors, are ubiquitous in laboratories throughout the scientific enterprise. Second, as science expands and the disciplinary boundaries blur, concepts originating in CMMP find increasing relevance to other physics subfields and other science disciplines, often forming entirely new research subfields (see Chapter 8). Scientific and technological connections between CMMP and atomic, molecular, and optical (AMO) physics are historically strong, principally because of similarities between the energy and length scales of the two fields. Laser and optical technology, developed primarily within the AMO community, has wide application in CMMP research for a variety of materials characterization and processing purposes. While lasers and optics have been the most prominent and wide-reaching connection so far, the recent development of methods to trap and cool atoms in the nano-kelvin regime also has the potential to profoundly affect CMMP by enabling the realization of some of the most fundamental models of condensed-
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Condensed-Matter and Materials Physics: The Science of the World Around Us matter physics. Conversely, emergent phenomena in interacting electronic and atomic systems from CMMP inspire new directions in AMO physics. Condensed-matter physics has significantly impacted nuclear and particle physics over the years, from studies of laboratory nuclei, to the study of neutron stars, to models of elementary particles. Such connections are not unexpected, since nuclei, as complex many-body systems, present intellectual challenges with many similarities to condensed-matter physics. The discovery of the Bardeen-Cooper-Schrieffer theory of superconductivity had an immediate impact on nuclear physics with Cooper pairing of neutrons and protons, thereby explaining many features of actual nuclear excitation levels. Further, the neutron matter that comprises neutron stars is expected to be superfluid, and the proton matter superconducting. The connections between CMMP and astrophysics instrumentation are also strong. Virtually every modern telescope has a sophisticated solid-state detector at its focus. At optical wavelengths, silicon charge-coupled-device arrays long ago supplanted photographic plates, as they have done recently in ordinary photography. Advances in solid-state devices are also having an immediate impact on increasing the resolution and the accessible space (time) range of astronomical observations. Advances in a number of areas of CMMP have had an important impact on developments in chemistry, especially in the areas of materials chemistry and physical chemistry. In the area of computation, density functional theory is now used extensively by chemists to calculate the electronic structures of materials and by polymer physicists to calculate the structure of polymer molecules in solutions and melts. CMMP has also had a huge impact through the development of advanced characterization tools, such as synchrotron light sources, neutron probes, scanning probes for studying the nanoworld of new materials, and nuclear magnetic resonance, which has become one of the most powerful characterization tools in chemistry and polymer science. The symbiotic nature of the relationship between CMMP and chemistry is reflected in the fact that synthetic chemists have enabled some of the most exciting advances in CMMP in recent years, such as the remarkable advances in conducting polymers, buckminsterfullerene (C60) and carbon nanotubes, lanthanum cuprate high-temperature superconductors, and MgB2, now being developed for use in advanced superconducting magnets for magnetic resonance imaging. The experimental methods of CMMP have also had an enormous impact on biology and medicine and have ushered in a new era of quantitative approaches to biological measurements and prediction. Biomolecular structures are now being catalogued through the use of technologies such as synchrotron radiation and x-ray crystallography developed in the CMMP community. Fundamental studies of energy transfer between two spins have allowed measurement of the distance between atoms in proteins even as the protein tumbles freely in solution. Magnetic resonance studies of proton relaxation in water have enabled detailed studies of
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Condensed-Matter and Materials Physics: The Science of the World Around Us neural activity and blood flow. Lasers in confocal microscopy systems, near-field optics, and scanning multiphoton fluorescence microscopies have made it possible to reach deep into tissues at the single cell level to study brain function and observe the dynamics of biological motion at the nanometer scale. In computer science, CMMP has also contributed enormously not only to the development of the hardware devices that implement information technology but also to the theory of computation and algorithms as well. First used in nuclear physics and further developed in CMMP, Monte Carlo methods, which compute properties by the judicious sampling of possibly favorable configurations, led to a new class of optimization and search algorithms in computer science. Correlation and scaling laws from statistical mechanics are used to describe and understand the structure and emergent behaviors of large computer networks. Concepts of self-organized collective behavior from CMMP are now at the frontier of computer science and robotics. The role of CMMP in quantum computing is even more central. The theory of the transmission and processing of intact quantum states has significantly altered the assessment of the kind and quantity of physical resources needed to solve various computational problems, with applications to cryptography and potential quantum computation. Moreover, CMMP research is contending to be the provider of the physical qubits for the hardware implementation of this new kind of computing. INDUSTRIAL RESEARCH In the United States, the once-great industrial laboratories, where much pioneering work was accomplished on semiconductors, computers, memories, and communications, have undergone major changes. The research funding from companies that had a de facto monopoly has significantly declined and in some cases disappeared. Many of the laboratories have been redirected, sold, or closed, and much of the fundamental work has ceased. With the remaining U.S. industrial laboratories often focused on much shorter-term goals, there is concern that the next great revolution in technology will be triggered by research developments elsewhere in the world. The industrial laboratories also served as incubators for scientific and technological leadership. Many of today’s leaders at the nation’s leading universities, national laboratories, and other institutions originated from the industrial laboratories, where they were able to establish their careers working on fundamental, high-risk problems with relatively little funding pressure. In spite of the differences between corporate and academic culture, the overall impact of these scientists on academia has been positive, and the source of such researchers is now drying up. As pointed out in this report, the rebuilding of industrial laboratories with the ability to do long-range research does not seem feasible on the timescale of the
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Condensed-Matter and Materials Physics: The Science of the World Around Us next decade. Global competition and the disappearance of industrial monopolies have changed the environment for industrial research. The replacement of the great industrial laboratories as sources of invention and leadership is a major challenge to the United States. The physics community, the federal government, and interested private-sector parties, such as investors in new technology, individual companies, foundations, and industrial consortia, must work together to create organizational and funding mechanisms that work well to create future technical breakthroughs and to provide the United States with a pathway for future scientific and technological leadership. A number of new approaches to long-term research are being explored to establish viable routes from fundamental CMMP discoveries to technological inventions to industrial leadership (as discussed further in Chapter 9). Based on the analysis of the quantitative data, the trends now occurring, and the various approaches now in progress, the committee sees the next decade as a period of great opportunity for developing new ways to increase economic growth through technological innovation and to improve the quality of life. STRUCTURE AND LEVEL OF THE CURRENT RESEARCH EFFORT To address its charge to examine the structure and level of the current research effort, the Committee on CMMP 2010 provides an overview of recent trends in CMMP regarding funding, demographics, and publications. The research funding for CMMP over the past 10 years shows a net increase of about 10 percent in inflation-adjusted dollars, using the Office of Management and Budget (OMB) deflators. But when analyzed using the average cost increase of about 5 percent per year per graduate student, the committee estimates that the buying power of research grants has decreased by about 15 percent over the past decade. As a result, most grants now allow support of one graduate student. In addition, there has been a dramatic decrease in the past 5 years in the chances of a grant application in CMMP being funded at the National Science Foundation’s (NSF’s) Division of Materials Research, from 38 percent in 2000 to 22 percent in 2005. For investigators who have not had NSF funding for the past 5 years, including new investigators, the situation is even bleaker, with a drop from 28 percent in 2000 to 12 percent in 2005. These low success rates speak to the hidden “overhead” of writing and reviewing proposals, lowering the efficiency of the scientific community and lowering the morale of new investigators. From these data, one can understand why many CMMP research groups in the United States are having a hard time participating in the exciting research opportunities (such as those described in Chapters 2 through 7 of this report). At the same time, China, Korea, Taiwan, and other countries show rapid growth in funding. Although CMMP remains the most popular subfield in physics, there has been a decline in the number of U.S. CMMP Ph.D. degree awards by 25 percent over
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Condensed-Matter and Materials Physics: The Science of the World Around Us the past decade. The extent to which this decline has been correlated with funding trends needs to be better understood. In fact, the whole physics community have suffered a corresponding percentage drop in their Ph.D. awards over this period. This is a matter of concern at a time when national policy makers have verbally encouraged increases in the training of science and engineering personnel. There has also been a decline in the fraction of U.S. publications compared with total publications in two major journals of CMMP worldwide (Physical Review B and Physical Review E), from 31 percent to 24 percent over this decade (see Figure 1.7). The major increase in the number of publications during this period has come from Western Europe, with strong increases from Asia and the rest of the world. These data show that CMMP is in general flourishing, with the overall number of publications doubling since 1993. The data, however, show that the United States has not been able to participate in the growth of the field. Further investigation of publication citation data shows that the United States continues to rank at about the same level that it was at 5 years ago in terms of the fraction of the top 100 most-cited papers per year. However, if other parts of the FIGURE 1.7 U.S. leadership in number of CMMP articles published in two leading journals, Physical Review B (PRB) and Physical Review E (PRE), is eroding. SOURCE: Publication data supplied to the Committee on CMMP 2010.
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Condensed-Matter and Materials Physics: The Science of the World Around Us world continue to outpace the United States in support for CMMP research, it will be difficult to recruit and retain top scientific talent in the United States. For the United States to remain competitive with the rest of the world in CMMP research, the committee believes that the present number of CMMP investigators should increase modestly for core CMMP activities and growth in new areas, and that the buying power of grants should be restored to their fiscal year 2000 levels at a minimum. An increase in funding (for example, 20 percent above inflation over the next decade) is also needed to allow for the nurturing of newly spawned frontier interdisciplinary areas connecting CMMP with other physics subfields (such as AMO physics), and with other science disciplines that are now merging strongly with CMMP at its boundaries, such as biology and chemistry. TOOLS, INSTRUMENTATION, AND FACILITIES FOR CMMP RESEARCH CMMP researchers have developed remarkable tools to uncover the microscopic origins of emergent phenomena. These tools were designed to observe, predict, and control the arrangements and motions of the constituents that comprise condensed-matter systems. The constituent particles span an enormous range of sizes—from electrons and atoms in semiconductor devices, to polymers in plastics, to bubbles in foams—and their motions span a correspondingly immense range of timescales. As a result, the experimental, computational, and theoretical tools required to study them are extremely diverse. Many of these tools are developed by individual research groups; other tools, such as synchrotron x-ray and neutron sources, are developed at large-scale national laboratory facilities. Measurement techniques designed to probe the properties of matter at smaller length, time, or energy scales, or with greater quantitative resolution and sensitivity, advance the forefront of CMMP research. Likewise, techniques designed to synthesize high-quality materials with precisely controlled structures underpin many great CMMP discoveries. By pushing the boundaries of materials fabrication and measurement forward, experimental CMMP researchers have uncovered new phenomena that were often unanticipated. These discoveries have not only transformed CMMP, but they have led in turn to new ways to manipulate and image matter, crucial to many new technological advances with a broad range of applications. As a result, the benefits of new techniques often stretch far beyond condensed-matter and materials physics. For example, the CMMP technique of x-ray diffraction, applied to DNA, led to the founding of molecular biology, and scanning probe microscopes have now evolved into universal tools at the nanoscale for the physical and life sciences. Experimental condensed-matter tools underlie many noninvasive medical diagnostics, while theoretical and computational tools from CMMP, such as local electron density approximations and numerical simulation methods, are now used to develop new
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Condensed-Matter and Materials Physics: The Science of the World Around Us pharmaceuticals. As CMMP researchers seek to answer fundamental questions about materials, they will continue to design tools that will benefit CMMP, other scientific disciplines, and also society. The discovery and synthesis of new materials are central to CMMP and to each of the six challenges identified in this report. The United States is no longer a leader in the creation of new materials and must recapture its lost status. The consequences of delay and neglect are long-term erosion of the U.S. international competitive edge and a loss of intellectual property. A National Research Council (NRC) study is now under way to determine how best to address the new materials synthesis challenge. The Committee on CMMP 2010 was specifically charged to look at facility and instrumentation needs for the future. To help address this charge, the committee convened a workshop in January 2007 to obtain broad input from the community. The resulting recommendations are focused on priorities for the next decade but with an eye toward further evolution of the facilities programs for the following decade because of the long time lines necessary for planning purposes. The workshop participants gave the committee a clear message that investment should also be spread across all the areas identified in this report and not concentrated on any one kind of facility. Balance is also needed between the support of facilities and instrumentation relative to the research programs of the individual research groups or small teams of investigators, remembering that CMMP is driven by the individual research groups. The U.S. light sources represent a large capital investment by the federal government to support advances in basic research. Light sources allow the extension of the power of the optical microscope to obtain images of condensed matter at much smaller distances in real space, as well as in the space spanned by momentum and energy, and in what is becoming increasingly important, a mixture of the two. The committee was impressed by the technological advances that had taken place in the past few years, and focused its recommendations on capturing the tremendous research opportunities seen for the coming decades. The U.S. capabilities in neutron scattering, including diffraction, reflectivity, time-of-flight, and small-angle scattering probes, are being greatly enhanced with the construction and commissioning of the Spallation Neutron Source. The committee’s recommendations are based on strategies to build on these investments and to exploit the capabilities of these new tools to understand properties at the nanoscale and to meet CMMP grand challenges. Electron microscopy, a basic tool for the characterization of materials, is utilized at the local level through central facilities that normally provide standard and high-end scanning and transmission electron microscopes, along with some support staff to facilitate their usage. Forefront instruments are available at Department of Energy national laboratories for sophisticated users through peer review
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Condensed-Matter and Materials Physics: The Science of the World Around Us evaluation of proposed research. Recently, great strides have been made with the development of aberration-free electron optics, thereby providing images with atomic resolution and putting the United States for the first time in many years in a competitive position in this research field. Recommendations aimed at strengthening the competitive position of the United States in electron microscopy techniques while supporting the needs of the CMMP research community are presented. High magnetic fields of 15 to 20 tesla are now available in many local laboratories through superconducting magnets. For higher magnetic fields, use of the National High Magnetic Field Laboratory is necessary. Not only does this laboratory provide a wide range of best-in-class static and pulsed magnets, but it is also the center for the development of the next generation of advanced materials (such as MgB2) for superconducting magnets and instrumentation for the entire suite of high-field magnets and associated facilities. The next decade is poised to see continuing gains in static and pulsed magnetic field capabilities as well as the utilization of high magnetic fields in conjunction with synchrotron and neutron-based probes to study selected frontiers of CMMP, as discussed in a recent NRC study.1 Computation has become an indispensable tool in all aspects of condensed-matter and materials physics theory and experiment. Maintaining and developing high-performance computing resources for condensed-matter and materials physics should continue to be a high priority. Computer time and scientific programming support should be available at a variety of levels, from centralized national supercomputer facilities to the state, local, university, and individual-research-group levels. The diversity of facilities and their distributed character make it difficult to track exactly what resources are available, and it is clear that lack of computational resources represents a significant bottleneck for some researchers, particularly junior university faculty members; attention to the improved distribution of resources could have a significant impact. CONCLUDING COMMENTS Moving into the 21st century, CMMP faces exciting scientific and technological opportunities, summarized in the six grand challenges identified in this report. These and other challenges will drive the continued vitality and growth of CMMP, as well as its continuing impact on the U.S. economy and society. The fundamental scientific questions, the close interplay between theoretical and experimental research, and the technological applications that will contribute to solving important societal problems all drive enthusiasm for the field. Attracted by such compelling research opportunities, more starting graduate students in U.S. programs choose 1 National Research Council, Opportunities in High Magnetic Field Science, Washington, D.C.: The National Academies Press, 2005.
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Condensed-Matter and Materials Physics: The Science of the World Around Us CMMP than any other single subfield of physics. These young minds are the future of CMMP and of its role in society. However, the Committee on CMMP 2010 also concluded that there are danger signs on the horizon. U.S. leadership in fundamental CMMP research is seriously threatened by the low success rates in proposals submitted for government funding of research, the precipitous decline of involvement of industrial laboratories in fundamental CMMP research, and the increasing competition from other countries for the best scientists. Due to tremendous momentum in the research establishment, the ill effects of these structural problems are only just starting to manifest themselves in measurable terms, such as publication rates, and in the ability to attract the best young scientists to research positions in the United States. The Committee on CMMP 2010 therefore urges that action be taken now. Prompt attention to these structural problems is needed to ensure U.S. leadership in CMMP research and technological innovation now and for the future.