BPA NEWS Board on and Astronomy • National Research Council • Washington, DC • 202-334-3520 • www.nas.edu/bpa • December 1998

als: How Science Improves our Lives, is industries. The years ahead promise Condensed-Matter and based on a workshop that the Committee equally dramatic advances, making this Materials Physics held in July, 1996. Copies are available an era of great scientific excitement for from the BPA office ([email protected]) and research in the field. Communicating by Venkatesh Narayanamurti, the report can be found on the web at this excitement and ensuring further Chair, Committee on Condensed- www.nap.edu/readingroom/books/ progress are the main goals of the Matter and Materials Physics physics/. CMMP report. The full report of the Committee Over the decade since the last major chair the Committee on Condensed- contains recommendations aimed at assessment of the field, important I Matter and Materials Physics continuing progress in the field. To be results and discoveries have come (CCMMP), which was commissioned by published early next year, the report will rapidly and often in unexpected ways. the Board on Physics and Astronomy to be the centerpiece of the Solid State These advances range from develop- prepare a volume on this field for the Sciences Committee Forum that will be ment of new experimental tools for survey Physics in a New Era. Our Com- held on February 16-17 in Washington atomic-scale manipulation and visual- mittee recently completed its report, and DC. [See the following article.] ization, to creation of new synthetic this article is based on its executive sum- Condensed matter and materials materials (such as bucky balls and high- mary. physics (CMMP) plays a central role in temperature superconductors), to In addition to myself, membership of many of the scientific and technological discovery of new physical phenomena the Committee included James B. advances that have changed our lives so such as giant magnetoresistance and Roberto, Gabriel Aeppli, Arthur dramatically in the last fifty years. the fractional . Bienenstock (who left the Committee to CMMP gave birth to the transistor, the An enormous increase in computing take up the position of Associate Director integrated circuit, the laser, and low- power has yielded qualitative changes in for Science at the Office of Science and loss optical fibers so important to the visualization and simulation of complex Technology Policy), J. Murray Gibson, modern computer and communication See “Condensed-Matter Physics” on Page 2 Steven Girvin, Mark Ketchen, Edward Kramer, James S. Langer, Cherry A. Murray, V. Adrian Parsegian, Paul S. Solid State Sciences Committee Plans Forum Peercy, Julia M. Phillips, Robert C. SSSC Forum to Feature Condensed-Matter and Materials Richardson, Frans Spaepen, and Katepalli Report at February, 1999 Gathering R. Sreenivasan. The CCMMP has already published a VERY few years the Solid State Sci- Materials Physics. CCMMP Chair pamphlet that describes some of the Eences Committee holds a forum in Venkatesh Narayanamurti will give an forefront areas of the field in language Washington for discussion and informa- overview of the report and its conclusions accessible to a broad audience. The tion exchange among researchers and and recommendations in the second pamphlet, entitled The Physics of Materi- policy makers. Forum participants in- session. Also included in this session will clude leaders from academia, industry, be perspectives of industry, universities, government laboratories, federal agen- and government laboratories. In this issue: cies, and the Congress. The 1999 Forum, The third session will address materi- to be held February 16–17 at the National als education and infrastructure as well as • Condensed-Matter and Academy of Sciences in Washington, will the challenge of providing facilities at all Materials Physics. Page 1 be entitled Materials in a New Era. scales. A member of Congress has been The final session will provide a vision • SSSC Forum. See article on invited to present the keynote address in of the scientific frontier, including an Page 1, Agenda on Page 4, and the opening session. In the first session, outlook for fullerene research presented tear-out Registration Form on agency leaders such as Martha Krebs, by Nobelist Richard Smalley of Rice Director of the newly-renamed DOE University. Page 5. Office of Science, will discuss the R&D For more details, see page 4. If you • Novel Quantum Phenomena. outlook from the point of view of the would like to attend, please return the Page 3 federal agencies. registration form on pages 5-6 of this The main focus of the forum will be newsletter as soon as possible. For the • Nuclear Physics. Page 9 the recently-completed report of the latest on plans for the forum, see the SSSC Committee on Condensed-Matter and web page, http://www.nas.edu/bpa/sssc.n 2 BPA News • December 1998

Condensed-Matter Physics (cont.) larly at the boundaries of disciplines, and to prepare flexible and adaptable physi- Board on Physics and Astronomy phenomena in large-scale many-atom cists for the future. systems. Progress in synthesis, visual- •Developing new modes of coopera- Robert C. Dynes, Chair ization, manipulation, and computation tion among universities, colleges, gov- University of California, San Diego will continue to impact many areas of ernment laboratories and industry to Robert C. Richardson, Vice Chair research spanning ensure the connectivity of the field with Cornell University different length scales needs of society and to preserve the fertile Steven Chu from atomic to macro- Research Themes in innovative climate of Stanford University scopic. Strong impact CMMP may also be expected in major industrial labora- Val Fitch · The quantum mechanics tories which have played “soft” condensed- matter physics, particu- of large, interacting a dominant role in Ivar Giaever larly at the interfaces systems. CMMP research. Rensselaer Polytechnic Institute with biology and chem- · The structure and proper- The different modes Richard D. Hazeltine istry. ties of materials at re- of research—benchtop experiments, larger University of at Austin The priorities of duced dimensionality. society are shifting from · collaborations, and so John Huchra Materials with increasing on—are evolving Harvard-Smithsonian Center for Astrophysics military security to levels of compositional, economic well-being steadily. The work that John C. Mather structural, and functional and health. Changing is carried on in these NASA Goddard Space Flight Center complexity. varied venues is com- societal priorities, in · R. G. Hamish Robertson turn, create shifting Nonequilibrium processes plex and diverse, and University of Washington demands on CMMP. and the relationship the Committee has paid special attention to Joseph H. Taylor, Jr. Among these growing between molecular and Princeton University demands are improving mesoscopic properties. describing the fore- public understanding of · Soft condensed matter fronts of research in Kathleen C. Taylor terms of a small number General Motors R&D Center science, better educa- and the physics of large of research themes. tion of scientists and molecules, including J. Anthony Tyson engineers for today’s These themes, listed in Lucent Technologies biological structures. employment market- the box at the left, are · Controlling electrons and George M. Whitesides place, and making new discussed in some detail Harvard University contributions to the photons in solids on the in the Overview and nation’s industrial atomic scale. reappear in each of the NRC Staff · competitiveness. Understanding magne- chapters of the report. Dr. Donald C. Shapero, Director The key challenges tism and superconductiv- One of the themes Dr. Robert L. Riemer, Associate Director facing condensed- that has captured the Dr. Kevin Aylesworth, Program Officer ity. matter and materials · Properties of materials imagination of theorists Dr. Joel Parriott, Program Associate and experimenters alike Grace Wang, Project Associate physics are: under extreme conditions. •Nurturing the · is the structure and Materials synthesis, properties of materials š intellectual vitality of processing, and the field—particularly at reduced dimensional- nanofabrication. ity—for example, in the facilitation of the · The Board on Physics and Astronomy is a research of individual Moving from empiricism planar structures. continuing interdisciplinary body with expertise investigators and small toward predictability in Large-scale integrated spanning the various subfields of physics, teams in areas that cross the simulation of materi- circuits depend on astronomy, and astrophysics. It serves as a focal disciplinary boundaries. als properties and pro- understanding the point in the National Research Council for issues behavior of semicon- connected with these fields. The activities of the •Providing the facili- cesses. Board are supported by funds from the National ties infrastructure for ductors in such configu- Science Foundation, the Department of Energy, the research—for example, creation of rations, so the potential Department of Defense, the National Aeronautics laboratory-scale microcharacterization for impact is apparent. and Space Administration, the National Institute of facilities at universities and large-scale A number of actions are required to Standards and Technology, and private and other maintain and enhance the productivity of sources. facilities at national laboratories. •Enhancing efforts in research uni- the field of condensed-matter and materi- versities to improve integration of als physics. These actions involve each CMMP education and research, particu- level of the hierarchy of research modali- BPA News • December 1998 3 ties and the interactions among the various Novel Quantum levels and the various performers. The Committees of the principal recommendations of the Com- Phenomena in mittee are summarized as follows. Condensed-Matter Board on Physics and •NSF, DOE, and other agencies that Astronomy support research should continue to Systems nurture the core research that is at the Committee on heart of condensed-matter and materials Steven M. Girvin Astronomy and Astrophysics physics. The research themes described Department of Physics John Huchra, Harvard-Smithsonian in the overview provide a guide to the Indiana University Center for Astrophysics, and Thomas forefronts of this work. Prince, Caltech, Cochairs •The agencies that support and direct 1 Introduction Committee on Atomic, Molecular, research in CMMP should plan for in- NE might imagine that, since con- and Optical Sciences creased investment in modernization of Odensed matter and materials physics Wendell T. Hill, III, University of the CMMP research infrastructure at deals with known objects (atoms) Maryland, Chair universities and government laboratories. interacting via well-defined and well- Committee on Gravitational Physics •The NSF should increase its invest- understood forces (the Coulomb interac- James Hartle, University of ment in state-of-the-art instrumentation tion among the charged particles), that California at Santa Barbara, Chair and fabrication capabilities, including there are no surprises and no fundamen- centers for instrumentation R&D, tal intellectual challenges left to be Committee on Nuclear Physics nanofabrication, and materials synthesis discovered. Nothing could be further John C. Schiffer, University of Chicago and processing at universities. The DOE from the truth. and Argonne National Laboratory, Chair should strengthen its support for such Quantum mechanics is a strange Physics Survey Overview Committee programs at national laboratories and business, and the quantum mechanics of universities. Thomas Appelquist, , large collections of atoms and molecules Chair •The gap in neutron sources in the can be stranger still. It inevitably happens should be addressed in the that, when assembling a collection of Plasma Science Committee short term by upgrading existing neutron atoms to form a material, the whole is Chuan Liu, University of Maryland, scattering facilities and in the longer term greater than the sum of the parts in the Chair by moving forward with the construction sense that emergent phenomena such as Solid State Sciences Committee of the Spallation Neutron Source. phase transitions (quantum or classical) Thomas P. Russell, University of •Support for operations and upgrades and spontaneously broken symmetries Massachusetts, Chair at synchrotron facilities, including re- often appear in large collections of atoms. search and development on fourth- For example, a set of widely spaced Committee on Condensed- generation light sources, should be copper atoms has an energy gap for Matter and Materials Physics strengthened. charge excitations and thus is an insula- Venkatesh Narayanamurti, Harvard •The broad utilization of synchrotron tor. This is because the atoms are largely University, Chair and neutron facilities across scientific independent of each other and retain the Committee on Radio Frequencies disciplines and sectors should be consid- discrete spectra of isolated atoms. Paul Steffes, Georgia Institute of ered when establishing agency budgets. Compressing the atoms into solid copper Technology, Chair •Federal agencies should provide causes the electrons to “melt” (even at incentives for formation of partnerships absolute zero) into a new “liquid” phase Helium Reserve Committee among universities and government and with no excitation gap and which is an John Reppy, Cornell, and Ray Beebe, industry research laboratories that carry excellent electrical conductor. If the same Homestake Mine (ret.), Cochairs out research in condensed-matter and experiment is carried out with aluminum Astronomy and Astrophysics materials physics. atoms, very subtle differences in the Survey Committee •Universities should endeavor to atomic properties lead not to an ordinary Joseph Taylor, Princeton University, and enhance their students’ understanding of metal, but rather to a superconductor. Christopher McKee, University of the role of knowledge integration and The idea of emergent phenomena California at Berkeley, Cochairs transfer as well as knowledge creation. In teaches us that, even though we under- this area, experience is the best teacher. stand and can relatively easily compute š Action on these issues will allow us to the properties of individual atoms, More information on BPA committees capture the opportunities for intellectual materials constructed from large collec- may be found on the BPA webpage at progress and technological impact that tions of atoms will routinely surprise us www.nas.edu/bpa/ continue to emerge in condensed-matter and materials physics. n See “Quantum Phenomena” on Page 7 Materials in a New Era The 1999 Solid State Sciences Committee Forum Lecture Room National Academy of Sciences Washi ng ton, D C February 16-17, 1999

Tuesday, February 16, 1999 Opening Session Welcome and Introduction – Thomas Russell, SSSC Chair A National Perspective on R&D – Rep. Vernon Ehlers Session I: Materials and the Federal Role Office of Science and Technology Policy – Arthur Bienenstock, Associate Director for Science National Science Foundation – Robert Eisenstein, Assistant Director for Mathematical and Physical Sciences National Institute of Standards and Technology – Raymond Kammer, Director Department of Energy – Martha Krebs, Director, Office of Science Department of Defense – Hans Mark, Director for Defense Research and Engineering National Institutes of Health – Ruth Kirschstein, Deputy Director Panel Discussion – Speakers and Congressional Staff Session II: Materials R&D: The Next Decade Report of the Committee on Condensed-Matter and Materials Physics – Venkatesh Narayanamurti, Harvard University Materials R&D in Industry – Cherry Murray, Lucent Technologies Changing Roles for Research Universities – David Litster, Massachusetts Institute of Technology Changing Roles for Government Laboratories – John McTague, Ford Motor Company Panel Discussion of the Future of Materials R&D Reception

Wednesday, February 17, 1999 Session III: Materials Education and Infrastructure Materials Education for the 21st Century – Robert Chang, Northwestern University Meeting the Challenge in Neutron Science – Bill Appleton, Oak Ridge National Laboratory Synchrotrons and the Next Generation Light Sources – David Moncton, Advanced Photon Source Smaller Facilities: Opportunities and Needs – J. Murray Gibson, University of Illinois at Urbana-Champaign Session IV: Materials R&D – A Vision of the Scientific Frontier The Science of Modern Technology – Paul Peercy, SEMI/SEMATECH Novel Quantum Phenomena – Steven Girvin, Indiana University Nonequilibrium Processes and the Mesoscale – James S. Langer, University of California at Santa Barbara Soft Condensed-Matter and Macromolecular Science – V. Adrian Parsegian, National Institutes of Health The Future of the Fullerenes – Richard Smalley, Rice University Open discussion: Issues and opportunities in CMMP ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○

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Quantum Phenomena challenge is the same in both fields This feature gives superfluid helium 3 however: to find correct descriptions of many novel properties since the state of (continued from Page 3) the physics that work over a wide range of the system is determined not just by the scales. complex phase of the condensate wave with completely unexpected properties. A There has been tremendous progress function, but also by the local orientation prime example of this is one of the biggest in the last two decades in the discovery of the pair angular-momentum vector. surprises of the last decade, high-tem- and study of a variety of novel quantum The exotic pairing state of helium 3 is perature . It is hard to phenomena in condensed matter and naturally connected with high-tempera- imagine a less likely candidate for a atomic systems. A few examples include: ture superconductors for two indepen- superconductor than an insulating superfluidity in 3He, high-temperature dent reasons. First it has recently been ceramic compound with properties superconductivity, Bose-Einstein conden- established via several ingenious experi- similar to those of a china coffee cup. Yet sation of alkali metals and spin-polarized ments that the pairing state in high- when chemically doped to introduce hydrogen, quantum magnetism and the temperature superconductors is d-wave charge carriers, these compounds not quantum Hall effect. Electron “wave ( l = 2 ), rather than the usual l = 0 (s- only superconduct, they do so at record guides” have been constructed and the wave). Unlike the case of helium 3 high temperatures. quantization of their electrical conduc- however, the direction of the angular The characteristic energy scale for tance in units of eh2/ has been ob- momentum is not free to change but is individual atoms is 1–10 electron volts served. It is now also possible to construct fixed by the underlying lattice. In fact, the (eV). However, as we look on larger mesoscopic metallic grains large enough d-wave is actually a standing wave with length scales at collections of atoms, the to be superconducting but small enough the angular positions of its anti-nodes characteristic energies become smaller that one can observe significant changes parallel to the axes of the square copper and smaller and the excitations become in transport properties depending on oxide planes. more and more collective in nature. At whether the number of electrons on the One novel feature of d-wave super- low energies the effective elementary grain is even or odd. conductivity is that non-magnetic degrees of freedom may be collective scattering by disorder and scattering at objects very different from individual 2 Superfluidity and Super- interfaces can be pair-breaking. This electrons and atoms, and their effective conductivity effect has recently come to the fore interactions may be very different from because of evidence that has been ob- the original “bare” Coulomb interactions. Superfluids and superconductors have tained suggesting that certain crystal faces This is the source of the surprises that the remarkable property of carrying of high Tc materials spontaneously break emerge. matter or charge currents completely time-reversal symmetry by nucleating an It is instructive to compare this frictionlessly. In helium 4, the atoms additional pairing channel (for which situation with that in high-energy undergo Bose-Einstein condensation and surface scattering is not pair-breaking) to elementary-particle physics. There we become superfluid a few degrees above form a complex gap function. know the effective degrees of freedom and absolute zero. In a superconductor, pairs The second similarity between the their interactions at low energies—it is the of electrons join together to form an oxides and superfluid helium 3 is that the world of atoms around us. The intellec- effective bosonic degree of freedom. In an coherence length (the size of a Cooper tual challenge is to understand degrees of ordinary low-temperature superconduc- pair) is very small, and is comparable to freedom at shorter and shorter length tor, these Cooper pairs of electrons have a the spacing between the particles (in this scales and higher and higher energy diameter which is much larger than the case the electrons). This may mean that scales. This is done by constructing high- spacing between the electrons. Hence it is the superconducting transition bears energy particle accelerators to act as not usually appropriate to view the closer resemblance to Bose-Einstein microscopes with ever greater magnifica- superconducting as condensation and certainly means that tion, or by study of extreme conditions in Bose-Einstein condensation, though it is fluctuation and correlation effects are astrophysical systems and the early closely related. much more important than in an ordi- universe. This is just the reverse of what is The Nobel Prize in Physics was nary superconductor. This is because done in condensed-matter physics where awarded in 1996 for the discovery of mean field theory relies for its validity on we strive to understand collective effects superfluidity in helium 3. This isotope of there being a very large number of at longer and longer length scales. The helium is a fermion and it is Cooper pairs particles within the volume occupied by analog of the particle accelerator is the of atoms that (barely manage to) con- each Cooper pair. refrigerator which lowers thermal energy dense at temperatures exceedingly close Understanding strong correlation scales and increases the distance over to absolute zero. Unlike the electrons in effects is an important challenge both for which particles suffer inelastic collisions. an ordinary superconductor which form the superconducting state and the very The analog of extreme astrophysical pairs in a state of zero relative angular unusual normal state in these materials. conditions is putting a sample in a momentum, helium-3 atoms pair in a p- l = At this point there is no clear understand- dilution refrigerator. The intellectual wave ( 1) angular momentum state. See “Quantum Phenomena” on Page 8 8 BPA News • December 1998

high-T materials. very large dissipation whose temperature Quantum Phenomena c (continued from Page 7) Study of the short coherence length dependence can then be followed over a and associated strong fluctuations of the significant range below the zero-field Tc. order parameter in high-T materials has It is now understood that the correct ing of the mechanism for high tempera- c led to some very interesting and funda- answer to our question is the affirmative. As ture superconductivity. (We do not know mental advances in statistical mechanics. the temperature is lowered, the highly for example whether the superconductiv- The theoretical ideas that have been fluctuating “tangled spaghetti” of vortex ity occurs because of, or in spite of, developed are of direct relevance to lines begins to exhibit collective correlations antiferromagnetism.) Indeed, it is not technological problems presented by the over a length scale x which diverges at a unreasonable to ask whether the phrase strong suppression of the critical current characteristic ‘vortex glass’ temperature T . “the mechanism” is even meaningful in g by magnetic fields. High-T superconduc- Associated with this diverging length is a this case. c tors are, because of their short coherence divergence in the effective collective pinning Superfluid helium 3 is a strongly −θ length, strongly type II. This means that barrier ε ~|TT− | . Below this correlated fermi liquid which just barely g an applied magnetic field penetrates the temperature the barrier is infinite and can manages to form Cooper pairs. It is not sample relatively uniformly inducing a not be overcome by (equilibrium) fluctua- yet clear how to describe the correspond- high density of vortex lines. tions. The linear response resistivity is thus ing strong correlations in high-tempera- Application of a current produces a truly zero, not merely small. ture superconductors. The strange driving force which pushes the vortices There exists a beautiful analogy properties of the normal state may mean sideways, leading to dissipation of energy. between the classical statistical mechanics of that the standard theory of fermi liquids Naturally occurring or artificially intro- fluctuating vortex lines and the world lines can not be used to describe them. If so, a duced disorder produces a random of quantum bosons moving in space-time. totally new paradigm must be developed. pinning potential which tends to resist the This analogy is quite precise and has proved We now have a good general understand- motion of the vortices. One of the deep extremely useful in advancing our under- ing of one-dimensional conductors. The questions about this random statistical standing of the statistical mechanics of this availability of exact or essentially exact mechanical system is the following. In the ‘tangled spaghetti.’ solutions in this special case shows us one limit of weak driving force, are the Because of the unusual “floppiness” of scenario by which the Landau theory of vortices perfectly pinned or not? That is, vortex lines in high-T materials (due to the fermi liquids can fail in strongly-corre- c is the linear response resistivity ever truly short coherence length, the extremely weak lated systems. Little success has yet been zero at any finite temperature? Or to put it coupling between copper oxide planes achieved however in seeking greater more colloquially, “Is a superconductor along the c axis, and the high temperature), understanding of these effects in higher in a magnetic field really a superconduc- random point defects are not very effective dimensions. tor?” at pinning. The pinning efficiency for Ideally, it will be possible to develop a For many years it was thought that extended columnar defects is much better. simple picture which captures the the answer to this question was no. The These can be constructed using the linear essential physics and which will allow us rate of vortex “creep” was known to damage tracks produced by heavy ions to construct new materials with even become extremely small at low tempera- from an accelerator. The quantum boson higher critical temperatures, perhaps even tures but it was believed to be thermally analogy clearly demonstrates the existence above room temperature. One of the activated giving a resistivity of the form of a phase transition in which the vortices lessons we have learned, however, is that −ε ρ /kTB can become localized by columnar pins there exist vast families of complex ~ e and hence never vanishing. leading to a state with truly zero resistivity in materials containing many atoms per unit The physical picture behind this phenom- linear response. cell, whose surprising properties are still enon is that there is a characteristic e extremely difficult to predict a priori. This energy barrier associated with the 3 Summary is an especially important challenge for random pinning which is finite and can be theoreticians in the coming decade. overcome by thermal fluctuations. High-temperature superconductivity The small size of Cooper pairs in In low-temperature superconductors is currently posing great challenges to high-temperature superconductors has this question, while important in prin- experimentalists and theorists alike. The the benefit that it (at least naively) ciple, is nearly moot in practice because 1998 Nobel Prize in physics was awarded increases their tolerance for very strong the barrier e tends to be large relative to for the discovery of another novel magnetic fields. However it also may be typical thermal energies at Tc and the quantum phenomenon, the fractional one of the (many) factors that limits the pinning is thus extremely effective at all quantum Hall effect. There are now well- critical currents in these materials. temperatures where superconductivity understood collective excitations of the Despite the technological problems exists. In high-Tc materials, the pinning coherent quantum electron fluid which caused by this latter effect and the difficult barrier e is smaller (another side effect of have the bizarre feature of carrying materials problems, progress is being the short coherence length) and Tc is fractional charge. More on this phenom- made toward practical applications of much larger. Hence magnetic fields induce enon in the next issue of BPA News. n BPA News • December 1998 9

for more critically addressing the struc- Nuclear Physics: The Core of Matter, the Fuel of Stars ture of nuclei and the properties of bulk John Schiffer, University of Chicago and Argonne National Laboratory nuclear matter. HE Committee on Nuclear Physics neutrinos from the Sun and cosmic rays, An area that at present is generating Twas commissioned by the Board on and in low-energy laboratory tests of intense interest is related to nuclear Physics and Astronomy to assess the field these symmetries. processes in the cosmos. Experiments of nuclear physics as part of the survey With recent developments on the measuring neutrinos from the Sun and Physics in a New Era. The committee rapidly changing frontiers in nuclear from cosmic-ray interactions in the consists of Sam Austin, Gordon Baym, physics, the Committee on Nuclear Earth’s atmosphere strongly suggest that Thomas Donnelly, Bradley Filippone, Physics is greatly optimistic about the neutrinos are massive, a result that would Stuart Freedman, Wick Haxton, Walter next ten years. Important steps have been imply new physics beyond the current Henning, Nathan Isgur, Barbara Jacak, taken in a program to understand the “Standard Model” of particle physics. Witold Nazarewicz, Vijay Pandharipande, structure of matter in terms of quarks and U.S. nuclear physicists, who have worked Peter Paul, and Steven Vigdor, and it is gluons. The United States has made two in the field since initiating the first chaired by me. The following is the major and far-sighted investments in this experiment more than 30 years ago, are Summary of our report. program. The Continuous Electron Beam currently partners in the Sudbury Nuclear physics addresses the nature Accelerator Facility (CEBAF) has recently Neutrino Observatory, the first detector of matter making up 99.9 percent of the come into operation and is now deliver- that will distinguish solar neutrinos of mass of our everyday world. It explores ing beams of unprecedented quality. It different types, or “flavors.” Such the nuclear reactions that fuel the stars, will serve as the field’s primary “micro- experiments are part of a larger effort to including our Sun, which provides the scope” for probing the building blocks of carefully test the Standard Model at low energy for all life on Earth. The field of matter such as the nucleons (protons, energies. The nucleus is a powerful nuclear physics encompasses some 3,000 neutrons) and the nuclei of atoms, at the laboratory for probing many of the experimental and theoretical researchers small length scales where new physics fundamental symmetries of nature, who work at universities and national phenomena involving quarks and gluons because it can magnify subtle effects that laboratories across the United States, and should first appear. It will provide new may hide beyond the direct reach of the the experimental facilities and infrastruc- insights into the structure of both isolated world’s most energetic accelerators. ture that allow these researchers to nucleons and nucleons imbedded in the Another frontier area is the study of address the outstanding scientific nuclear medium. The Relativistic Heavy how the nucleus changes when subjected questions facing us. The CNP report Ion Collider (RHIC), whose construction to extreme conditions, such as very rapid provides an overview of the frontiers of is now nearing completion, will produce rotation or severe imbalances between the nuclear physics as we enter the next the world’s most energetic collisions of numbers of neutrons versus protons. millennium, with special attention to the heavy nuclei. This facility will allow Exotic nuclei play essential roles in the state of the science in the United States. nuclear physicists to probe the properties evolution of our galaxy: the “parents” of The current frontiers of nuclear of matter at energies and densities similar about half of the heavy elements are very physics involve fundamental and rapidly to those characterizing the cores of neutron-rich nuclei, believed to have been evolving issues. One is understanding the neutron stars and the Big Bang. RHIC created within the spectacular stellar structure and behavior of strongly experiments should teach us about the explosions known as supernovae, at interacting matter in terms of its basic expected transition to a new phase of temperatures in excess of a billion constituents, quarks and gluons, over a nuclear matter in which the quarks and degrees. Remarkable advances in wide range of conditions—from normal gluons are no longer confined within accelerator technology have now pro- nuclear matter to the dense cores of nucleons and mesons. vided the tools needed to produce such neutron stars, and to the Big Bang that The theory supporting these new unusual nuclei in the laboratory, opening signalled the birth of the universe. efforts has produced new bridges between the door to new experiments on the Another is to describe quantitatively the quantum chromodynamics (QCD)—the properties of nuclear matter near the properties of nuclei, which are at the theory of quarks and gluons—and the limits of binding. centers of all atoms in our world, in terms field’s more traditional models of nuclear The recommendations by this of models derived from the properties of structure, which involve nucleons and committee should be considered in the the strong interaction. These properties mesons. Nuclear theorists have begun to context of the careful planning in the include the nuclear processes that fuel the construct “effective theories” that are nuclear physics community summarized stars and produce the chemical elements. equivalent to QCD at low energies, yet by the long-range plans developed by the A third active frontier addresses funda- share many of the properties of tradi- Nuclear Science Advisory Committee mental symmetries of nature that mani- tional models that view nuclei as quantum (NSAC). NSAC advises the two principal fest themselves in the nuclear processes in fluids of protons and neutrons. This funding agencies for this field, the the cosmos, such as the behavior of work is providing the field with new tools See “Nuclear Physics” on Page 10 10 BPA News • December 1998

Nuclear Physics within the nuclear physics community, technical capabilities, a rich scientific the Committee on Nuclear Physics chose harvest is limited by severely constrained (continued from Page 9) to emphasize the science rather than the budgets. The committee recommends process in the recommendations pre- the near-term allocation of resources Department of Energy and the National sented below. However, it would be needed to realize these unique experi- Science Foundation. The Division of remiss if it failed to bring into focus the mental and theoretical opportunities. Nuclear Physics of the American Physical funding stresses that now severely Careful laboratory measurements of Society also played an important role, threaten the field. nuclear reactions that take place in stars joining with NSAC to organize various At present it seems to be generally have provided the foundation for some of town meetings for the purpose of gather- agreed by policymakers on all sides that the field’s most important achievements ing input from the community. The the support of basic research is in the in understanding the nuclear bases of the NSAC long-range plans have been public interest, and there is considerable cosmos, including the solar neutrino prepared at about 6-year intervals (1979, talk of increasing the corresponding problem and the origin of the light 1983, 1989, and 1996). They have been budgets. However, the reality in nuclear chemical elements in the Big Bang. influential in expressing new priorities of physics, as in many other fields of Beams of exotic short-lived nuclei are the field and in justifying new initiatives. research, is quite different. In 1996 the opening up new opportunities for The 1979 and 1983 long-range plans, for budget guidance provided by the DOE measuring nuclear properties and example, identified CEBAF and RHIC as and NSF to help formulate the most reactions in the poorly understood the most promising new initiatives for recent Long Range Plan for nuclear regions near the limits of stability. The decisively advancing the scientific physics was for roughly constant man- properties of these barely stable nuclei frontiers of the field. The recent adoption power budgets. This goal has been have direct quantitative connections to of a similar planning process by the undercut by the budgets of recent years. the processes that fuel the stars and create European nuclear physics community is The cumulative result of a dollar-flat the chemical elements of our world. an indication of the perceived effective- budget in the case of the DOE is that it Beams of exotic nuclei hold great promise ness of the long-range plans. now is 3 to 10 percent below the range of as tools for probing new nuclear proper- In parallel with CEBAF and the the guidance. In the case of NSF, there ties and in testing fundamental symme- construction of RHIC, the NSAC long has been a larger decline, to about 15 tries at low energies. These consider- range plans have also identified and percent below the 1996 guidance. ations provide a compelling argument for recommended several smaller targets of These decreases will curtail the constructing a next-generation facility opportunity. Among those currently utilization of new facilities and instru- that will use isotope separator online being implemented with agency funding mentation, and jeopardize our nation’s (ISOL) techniques to produce high- are an upgrade to the capabilities for world-leading role in the field. This intensity, high-resolution beams of short- producing energetic beams of short-lived situation has arisen even as the efficient lived nuclei over a broad mass range. nuclei at Michigan State University, the commissioning of CEBAF, the approach- Recommendation II: The committee construction of new detectors for study- ing completion of RHIC, new technical recommends the construction of a ing solar neutrinos, and the adaptation of advances in the exploration of nuclei near dedicated, high-intensity accelerator RHIC to the investigation of previously the limits of binding, and discoveries in facility to produce beams of short-lived inaccessible aspects of the proton’s low-energy neutrino physics have made nuclei. Such a facility will open up a new structure. execution of the 1996 Long Range Plan all frontier in nuclear structure near the Both the Department of Energy and the more urgent, requiring the level of limits of nuclear binding and will the National Science Foundation support funding given in the guidance by the strengthen our understanding of nuclear user facilities of world-class capability and agencies. properties relevant to explosive nucleo- both have strong university programs. Recommendation I: Discoveries in synthesis and other aspects of the physics DOE supports the largest user facilities nuclear physics—new phenomena governing the cosmos. and university groups, while NSF sup- connected with the role of quarks and Frontier research in nuclear physics ports user facilities at universities and gluons in the nucleus, the structure and relies on both large accelerators, such as many university user groups. The dynamics of nuclei, the nuclear physics CEBAF and RHIC, and smaller facilities, committee believes that the continuing of the cosmos, and the limits of the where specialized low-energy measure- programs in the two agencies are essential Standard Model—are within reach due ments can be made. These smaller to the field, with the DOE emphasis on to our recent investments in new facili- facilities include several university and national laboratory facilities and the NSF ties and instrumentation. With CEBAF national laboratory accelerators where emphasis at the universities providing having started on its research program of weak interaction, nuclear structure, and complementary strengths and opportuni- the quark-gluon structure of matter, nuclear astrophysics studies are done. ties. RHIC about to embark on the study of Both small and large accelerators rely Because there exists a tradition of matter at the limits of energy density, critically on innovative instrumentation successful deliberation and planning and with other recent advances in to make new discoveries. In the case of BPA News • December 1998 11

CEBAF and RHIC, the quality of the ered in the United States. densities for studies of fundamental physics programs depends on specialized RHIC is about to open a new door to symmetries. The committee recom- detectors. The development of much of ultra-high energy densities in nuclear mends the continuation of frequent this equipment is on a scale that is suitable matter. The potential discovery there of NSAC long-range plan efforts to help for university laboratories, where gradu- a new phase of matter—a plasma of retain the responsiveness of the field to ate students can participate in the quarks and gluons—could point the the most promising new opportunities. construction and gain experience with way to issues requiring still higher beam Nuclear physics not only advances the cutting-edge technology. Many of the intensities or energies. Construction of frontiers of knowledge but also makes equipment needs at the smaller facilities the Large Hadron Collider (LHC) at remarkable contributions to the needs of are equally specialized. Examples include CERN in Europe has recently begun, society. The generation of nuclear atom and ion traps designed for precision with U.S. participation. Early in the energy, both for civilian power consump- studies of weak interactions and sensitive next century, this facility will allow tion and for nuclear weapons, has had a detector arrays for measuring nuclear collisions of nuclei at 40 times the beam profound impact on our society in the last reactions at the very low energies charac- energy of RHIC. Future discoveries at 50 years. Equally far-reaching has been teristic of stars like our Sun. RHIC will guide upgrades of RHIC and the impact of nuclear physics in medicine; Recommendation III: The committee the participation of U.S. nuclear results of nuclear physics and nuclear recommends continued investment in physicists in the LHC effort. physics techniques, from magnetic instrumentation for research. As new The impact of the discovery that resonance to detector technologies to the discoveries come to light and new ideas neutrinos may have mass will be felt use of isotopes, have led to remarkable for experiments emerge, upgrades of throughout physics. Thus, following advances in diagnostic and therapeutic detector systems at CEBAF and RHIC, the Sudbury Neutrino Observatory power. Nuclear diagnostic techniques and instrumentation needs at smaller (SNO), there may be an urgent need to have a growing and pervasive role in laboratories should be considered in develop and deploy detectors capable of industry, national security, nonprolifera- accordance with their potential for new exploring the spectrum of lower-energy tion, geophysics, global climate research, discoveries. NSAC is well positioned to solar neutrinos, or of greatly improving and paleontology. Nuclear physics is the provide DOE and NSF appropriate the sensitivity to neutrinos from the basis of important technologies in the advice on relative priorities and specific next supernova neutrino burst. Terres- design and preparation of materials. major upgrades. trial neutrino experiments have put Through such applications, through the To foretell the course of a science important constraints on neutrino technical and intellectual intersections of beyond the near term is always difficult, properties; a compelling case may arise nuclear physics with other fields of as it depends both on the discoveries of for new terrestrial experiments. science, and through its intrinsic intellec- the next few years and the doors that Studies of fundamental symmetries in tual challenges, nuclear physics stands as new advances in technology will open. nuclei can isolate and enhance new one of the core sciences in continuing The following represents some of the phenomena beyond the Standard Model. advancement of knowledge. future options, among a number of In particular, new experimental searches Facilities and instrumentation are attractive possibilities that can be for a neutron electric-dipole moment and essential for progress, but science ulti- perceived at the present time, for precision measurements of beta-decay mately depends on the people who carry possible implementation in the early correlation coefficients can become the it out—on their individual creativity, part of the next century. most stringent constraints on our drive, and enterprise. The scientists who CEBAF probes nuclei at length understanding of fundamental symme- conduct experiments and develop the scales where the quark and gluon tries. Promising possibilities exist for theoretical framework for interpreting the substructure of nuclei should first developing sources of cold and ultracold results are the most essential components become apparent. It thus represents a neutrons of unprecedented intensity of the field. The continued intellectual first step in probing the relationship Recommendation IV: Within the vitality of nuclear physics as a science, and between standard nuclear physics based ten-year time frame envisioned for this the continuation of the field’s more direct on protons, neutrons, and mesons; and report, new discoveries will provide contributions to societal needs, depend the underlying fundamental degrees of strong arguments for one or more major critically on the capacity to educate the freedom—quarks and gluons. To new endeavors. Possible candidates next generation of physicists. Past understand the transition between these include a higher-energy electron ma- performance has demonstrated that regimes, it may be necessary to extend chine, capability for the study of heavy- students trained in solving the enor- the measurements to even finer resolu- ion collisions with increased energy mously challenging problems of forefront tion, such as that offered by a 15- to 30- densities, new detectors to explore mass physics research develop the array of GeV electron accelerator. The con- effects on the solar and supernova skills needed to lead the nation in har- struction of a 25-GeV machine is now neutrino fluxes, and an ultracold nessing the rapidly advancing technology under discussion in Europe, and future neutron facility providing an order-of- that often emerges from the research upgrades of CEBAF are being consid- magnitude increase in the neutron itself. n

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