Condensed-Matter Physics (1986) / Chapter Skim
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I Highlights, Opportunities, and Needs
I Highlights, Opportunities, and Needs
Pages 1-36
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The interface between physics and technology will receive fuller treatment in another volume in this survey.
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It has been the source of such extraordinary technological innovations as the transistor, 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.
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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 converters 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.
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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 spectroscopy (XPS)
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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.
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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 dimensionality systems important in technology, an example that has been vital to the physics of disordered systems as well.
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Experimentally, the study of localization is much clarified by using a two-dimensional geometry, in which one often sees a unique nonclassical behavior of the electronic conductivity, and by technical advances 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 hightemperature 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
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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.
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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 quantummechanical laws of Bose statistics, whereas 3He obeys Fermi statistics, the same as electrons.
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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.
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Synchrotron 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 experimental studies of condensed matter was the development of several probes capable of seeing individual atoms.
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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 investigations 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, lowenergy electron diffraction, electron energy loss spectroscopy, and atomic diffraction.
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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 conventional methods of solid-state physics are no longer applicable in determining their physical properties.
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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)
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Applications of femtosecond laser spectroscopy to studies of condensed 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.
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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.
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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
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Solid State Communications.
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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 technological manpower in an area with important implications for the electronics industry and national security.
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However, as an illustration of recent trends, the Division of Materials 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.
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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 experimental 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.
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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 equipment is being used and employ it productively, they must be trained in its use while graduate students.
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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.
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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.
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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, however, is not great, even though the return on the investment is large.
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The United States currently has two pulsed spallation sources. The Los Alamos Neutron Scattering Center (LANSCE)
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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.
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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.
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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.
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By contrast, occasional users have research programs based on other techniques, usually at their home laboratories, 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.
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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.
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However, if the strongest possible coupling between universities, government 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 increase the research cooperation between the national laboratories and university scientists, since special facilities exist at the national laboratories that are not available elsewhere.
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OPPORTUNITIES. A ND NEEDS 35 Formulate cooperative research projects with graduate students (e.g., the MIT-AT&T Bell Laboratories program)
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