Condensed Matter Physics1

Condensed Matter Physics at JHU The condensed matter physics research in the department is focused on studies of magnetism, critical phenomena, transport properties, pattern formation, nonequilibrium processes, artificially structured solids, low dimensional solids, heavy fermion systems, low temperature physics, neutron diffusion, and high Tc superconductivity. In recent years, the program has involved studies of the magnetic behavior of ultra-thin epitaxial films of iron, the magnetic and transport properties of vapor- deposited amorphous metallic solids, compositionally modulated solids, granular metals and metal superlattices, quasi 1- dimensional magnetic systems, heavy fermion systems, and the families of new high Tc oxide superconductors. Techniques used in these studies involve M”ssbauer spectroscopy, LEED and Auger electron spectroscopy, He3 -He4 dilution refrigerator, neutron diffraction resistivity measurements, magnetic susceptibility, vibrating sample magnetometer, SQUID magnetometry, ferromagnetic resonance, X-ray and electron diffraction spectroscopy, scanning electron microscopy, and transmission electron microscopy. A molecular beam epitaxy system and high-rate sputtering systems, in addition to single-crystal growth are used for sample fabrication. Electron Spectroscopy Group at Brookhaven National Laboratory Welcome to the home page for the Electron Spectroscopy Group at Brookhaven National Laboratory on Long Island, New York. The Electron Spectroscopy Group in the Condensed Matter Physics and Materials Science Department is composed of two main areas: angle resolved photoemission spectroscopy (ARPES) and infrared spectroscopy as a probe of the optical properties and complex conductivity of solids. The Electron Spectroscopy Group’s primary focus is on the electronic structure and dynamics of condensed matter systems. The group carries out studies on a range materials including strongly correlated systems and thin metallic films. A special emphasis is placed on studies of high-Tc superconductors and related materials. The primary techniques used include high-resolution photoemission and infrared spectroscopy or optical conductivity. The experiments are carried out both within the laboratory in the Physics Department and at the National Synchrotron Light Source. The emphasis is on the study of the lowenergy excitations and the nature of the interactions of the latter with their environment. The group has also established a successful pulsed laser deposition facility for the study of thin films. Future plans involve studies of nanoscale systems and will involve close collaboration and work within the newly created Center for Functional Nanomaterials. A brief survey of current research topics include:ARPES and infrared studies of electron and hole-doped igh-temperature superconductors Charge ("stripe") order in the nickelates Correlated electron systems hexaborides, etc.) Colossal magneto resistance in the manganates High-dielectric constant materials Single-wall carbon nanotubes Density-functional theory ab-initio calculations of electronic band structure and lattice dynamics of perovskites Condensed Matter, Solid State, and Materials Research Research topics in this diverse area range from innovative studies of the basic properties of condensed-matter systems to the nanofabrication and study of advanced electronic, optoelectronic, spintronic, and quantum-superconductor devices. Modern materials (especially those involving thin films) are increasingly produced in configurations in which the functionality and limitations of systems are determined by their surface or interfacial properties and by the structure and nature of atomic defects at these surfaces and interfaces. In applied physics, investigations directed at the physics of surfaces and interfaces include the study of catalysis and surface reactions, atomic resolution of the interface and grainboundary structure of electronic materials, and determination of the effect of a single atomic defect on electronic transport across an interface. Materials systems that are currently the focus of substantial research efforts by applied physics research groups include: silicon and related materials for semiconductor materials physics and nanoelectronics research; thin films of complex oxides for colossal magnetoresistance materials, high K dielectrics, and fundamental studies of thinfilm growth; heterostructures of III-V compounds and alloys, including gallium arsenide and various phosphides and nitrides, for experiments that use or elucidate effects of quantum confinement and seek to optimize carrier transport and optical properties for use in millimeter-wave transistors and ultra-high-speed optoelectronic devices; and low-temperature and high-temperature superconductor thin-film materials for research activities that seek both to clarify basic questions regarding superconductivity and to advance the prospects for significant applications of superconducting films and devices. Research groups in the field of applied physics employ a wide range of experimental approaches in the study of condensed matter physics and materials science. These include x-ray and electron diffraction, photoluminescence and Raman scattering, x-ray and optical spectroscopy, electron microscopy (particularly ultra-high-resolution electron microscopy and analytical electron microscopy), Rutherford ion-backscattering spectroscopy, tunneling spectroscopy, scanning probe microscopy, nanostructure transport studies, molecular-beam epitaxy with atomic-layer control, organometallic vapor-phase epitaxy, laser ablation, ultra-high-vacuum processing, electron-beam lithography, ion-beam lithography, and ion-beam processing. Field members continue to lead in the development of many of these experimental approaches.

Scientists win 'ultimate prize' in condensed matter physics Physics professor Nicholas Read and his colleagues have received the 2002 Oliver E. Buckley Condensed Matter Prize for their outstanding theoretical or experimental contributions to condensed matter physics. "It's great to have recognition for work that's part of our general attempt to understand how matter behaves under different conditions," says Read, professor of physics and applied physics. "This is one of the most prestigious awards in the field of condensed matter physics." The prize was endowed in 1952 by AT&T Bell Laboratories (now Lucent Technologies) as a way of recognizing outstanding scientific work. It is named in memory of Oliver E. Buckley, former president of Bell Labs. The other Buckley Prize recipients are Jainendra Jain of Pennsylvania State University and Robert Willett of Lucent Technologies. Eighteen previous Buckley Prize winners went on to win the Nobel Prize. According to Ramamurti Shankar, chair of the Department of Physics, the theoretical condensed matter physics program at Yale has grown enormously over the last 15 years. "Nick's receiving the ultimate prize in condensed matter physics is a richly deserved honor. Co-recipient Jainendra Jain also began his work on this problem when he was a postdoctoral fellow at Yale. The two departments [of physics and applied physics] are very proud to have been able to provide such a climate for research." Condensed matter physics underlies all modern electronics and led to the original invention of the transistor, which is the basis of semiconductor and computer technology. Read's Buckley Prize is for work published in a 1993 issue of Physical Review. His research focuses on quantum mechanics and semiconductors, which make up computer chips, the basis of all home electronics. Earlier studies have shown that it's possible to fabricate a small device or chip in which electrons move in two dimensions. "It's as if they're little billiard balls moving on a pool table," Read says. "There are billions of electrons inside a typical chip and they're moving around as if they're on a table in two dimensions." Electrical measurements can be made on this two-dimensional system of electrons, explains Read, and this can be done at very low temperatures -- close to absolute zero degrees Kelvin. When the chip is put into a magnetic field that is perpendicular to the two dimensions of the electrons, new states of matter can be observed. "Like molecules of water that can condense as a liquid when cooled below the boiling point, the electrons in two dimensions in a magnetic field can enter a new liquid state of matter when the temperature is very low," says Read. "Surprisingly, our new liquid state is similar to what happens to the electrons in metals."

Theoretical Condensed Matter Physics At the beginning of this 21st century, the field of condensed matter physics has grown to encompass an extraordinary range of topics that go far beyond its original roots in solid state physics and statistical mechanics. As a result, condensed matter physics has become the largest and one of Recent work by condensed matter theorist Professor the most exciting areas of physics Harold Baranger was motivated by experiments on quantum dots, which were created by using metallic to work in. A PhD in condensed matter theory provides an excellent gates on a GaAs/AlGaAs heterostructure to create a confinement potential and tunneling contacts to background to work on many leads. A schematic of a dot and its gates is shown in topics not just in physics but in other disciplines such as biology, (a), where the letter D denotes the dot and the numbers label the gates. The calculated conductance chemistry, computer science, economics, electrical engineering, through a stadium-shaped quantum dot is shown below in (b). A line of height G is placed for each and medicine. Despite the energy level in the dot. The conductance depends on enormous breadth of condensed the coupling of the wavefunction through the matter physics, nearly all theoretical work revolves around a tunneling barrier to each lead. Note the oscillatory envelope in the heights--this is produced by the central theme of understanding horizontal classical periodic orbit, a ``quantum collective phenomena: how chaos'' effect--as well as the fine-scale apparently complex properties of a system arise from parts which themselves random quantum variation--an example of ``mesoscopic fluctuations''. [From E. E. Narimanov, do not possess these properties. Thus the conduction electrons in a et al., Phys. Rev. Lett. 83, 2640 (99).] metal like lead are rather simple objects that can be characterized individually by their mass, charge, position, and velocity. Yet when lead is cooled below about 7o K, something neat and unexpected happens and these electrons organize themselves into a remarkable superconducting state in which electrical currents can flow forever and magnetic fields are excluded from the bulk of the metal. Modern condensed matter physics and many other areas of science are full of these "neat and unexpected" collective phenomena and efforts to understand them theoretically often generate deep and broadly useful insights that can be applied to problems far removed from the experimental data that originally motivated the theory.

Theoretical research at Duke reflects the great diversity of condensed matter physics. About half the condensed matter theory faculty work on topics related to collective properties of many-electron systems, especially at the frontier of nanoscience in which novel properties arise in electronic systems such as quantum dots that range from 1-100 nanometers in size. (As you may know, nanoscience has been identified as one of the scientific and technological frontiers of 21st-century research because of its importance to computers, biology, electronics, optics, and material design.) Nanophysics issues of current interest to the group include the interplay of interactions and interference in quanutm dots, novel many-body ground states, and magnetic nanoparticles.The other half of the faculty works on collective properties of classical systems for which quantum mechanics plays little if any role. These faculty use their condensed matter training to understand difficult equilibrium materials such as a spin glass, or the complex dynamical behavior of nonequilibrium media such as a convecting fluid, a laser, heart muscle, or a granular medium, or the properties of discrete interacting agents such as sellers and buyers in a model of an economic system. Despite the fact that quantum mechanics is not involved, many of the same kinds of issues arise as in electronic systems of how to characterize, understand, and predict the spatiotemporal structure of these systems.

FACULTY RESEARCH INTERESTS Professor Harold U. Baranger (Ph.D. Cornell University, 1986) is interested in Nanophysics--the physics of small, nanometer scale, bits of solid. Fundamental interest in nanophysics stems from the ability to control and probe systems on length scales larger than atoms but small enough that the averaging inherent in bulk properties has not yet occurred. Using this ability, entirely unanticipated phenomena can be uncovered on the one hand, and the microscopic basis of bulk phenomena can be probed on the other. Additional interest comes from the many links between nanophysics and nanotechnology. One of Dr. Baranger's recent projects involves the interplay between quantum interference and electron-electron interactions in quantum dots. A second long-term project is "quantum-chaos": how are quantum properties of a nanoparticle influenced by chaos in its classical dynamics. This project has lead to a secondary interest in wave-interference in all kinds of media, for example, the propagation of microwave signals inside buildings in connection with wireless communication. Future projects may include transport in nanoscale magnetic materials ("spintronics"), conduction through single molecules, and the combining of wave-interference physics with information theory in wireless communication. Visiting Assistant Professor Robert G. Brown (Ph.D. Duke, 1982) is interested in using algebraic and statistical methods to study a wide range of equilibrium and nonequilibrium problems. With collaborator Dr. Mikael Ciftan, Dr. Brown has developed new Monte Carlo Langevin equation-based techniques that allow dynamic/nonequilibrium and static/equilibrium phenomena to be studied on the same footing. His recent work includes algebraic and computational studies in dynamic and static critical phenomena in quantum optics and magnetism. In earlier work, Dr. Brown also developed a generalized (non-muffin-tin) stationary multiple scattering theory, including applications to band theory and quantum chemistry. This work formally

eliminates the muffin-tin approximation from KKR-type band theory and its equivalents in quantum chemistry, without the need for so-called "near field" corrections. Adjunct Professor Mikael Ciftan (Ph.D. Duke, 1968) is also on the faculty of the Army Research Office in Research Triangle Park. He is developing the coherent state functional integral method and applying it to many interesting problems in condensed matter physics and quantum optics. This approach uses group theory to simplify the daunting problem of evaluating real time - real temperature solutions in statistical mechanics. In particular, his interests embrace applications of physics at very small distances and time scales relevant to new computer technologies. His past accomplishments include some of the original experimental work with lasers and quantum spectroscopy and studies of super radiance and optical bistability in quantum optics. Professor Henry S. Greenside (Ph.D. Princeton, 1981) is interested in the rich collective dynamics of large sustained nonequilibrium systems and especially in spatiotemporal chaos (chaotic systems which are spatially disorganized) which occurs widely in fluid, chemical, laser, and biological systems. His current research involves trying to understand quantitatively recent high-precision experiments on Rayleigh-Benard convection, which is a central paradigm for physicists interested in understanding the fundamental properties of nonequilibrium systems. In collaboration with researchers in Duke's Department of Biomedical Engineering and Department of Psychiatry, Dr. Greenside is also interested in using theoretical insights from convection and other desktop systems to understand some difficult dynamical medical questions such as the onset and prevention of ventricular fibrillation in the heart and epilepsy in the brain. Associate Professor Konstantin Matveev (Ph.D. Institute of Solid State Physics, Russia, 1991) works on the theory of electronic transport in mesoscopic systems. Mesoscopic physics is a new area of research which studies various phenomena in very small conductors, with sizes typically on the scale of 1 micron or smaller. The interest in electronic properties of small conductors is strongly stimulated by the rapid progress of computer technology, where the transistor size has shrunk steadily in order to increase the processing speed and device density. The physics of mesoscopic conductors is very different from that of larger systems. First of all, the sizes of mesoscopic samples are so small that the quantum interference of electrons scattering off of impurities becomes essential and gives rise to a number of new phenomena. Secondly, the interactions between the electrons in small systems become stronger and often affect the flow of electrons dramatically. The interactions lead to a number of fascinating new phenomena, such as Coulomb blockade, which is interesting from both a fundamental point of view as a new way to observe the discreteness of charge, and as a new principle for building ultrasmall computer logic circuits. Professor Richard G. Palmer

(Ph.D. Cambridge, 1973) carries out research concerning various types of complex systems. He develops and uses techniques of statistical mechanics, stochastic processes, dynamical systems theory, and computer simulation. His interests include glasses and spin glasses, neural networks, genetic algorithms, evolution, and economic markets. His is currently working on (1) theoretical models to explain the paleontological extinction and speciation record; (2) simulations and analysis of 2d spin glass ground states; and (3) rugged landscapes with controllable neutrality. His long-term goal is to establish a firm theoretical foundations for understanding the emergence of structure, complexity, and computational ability in driven systems. Associate Professor Joshua E. S. Socolar (Ph.D.\ University of Pennsylvania, 1987) is interested in the principles that determine collective behavior in condensed matter and dynamical systems. His current research interests include: The spatial distribution of stresses granular materials (e.g. bins of sand, coal, pills, or grain) and jamming phenomena; Controlling chaos, or understanding feedback mechanisms that can stabilize otherwise unstable ordered behavior in chaotic dynamical systems; and selforganization and function of complex dynamical networks, especially genetic regulatory networks. He has also worked extensively on the physics of quasicrystals -- materials with quasiperiodic atomic structures akin to the Penrose tilings -- and on spatial structure in self-organized critic

Ventricular fibrillation, a medical condition that kills over 200,000 people each year in the United States, has attracted the attention of condensed matter theorists at Duke University who would like to understand how and why ventricular heart tissue will sometimes change from its normal time-periodic spatially-coherent beating to an abnormal nonperiodic spatially-disordered state such that the heart can not pump blood effectively, causing death if not immediately treated. This figure shows a snapshot from a computer simulation by graduate student Elizabeth Cherry, and Professor Henry

Greenside who have invented a powerful space-time-adaptive computer code for simulating three-dimensional heart dynamics in domains large enough and over times long enough to study the transition to fibrillation. The figure shows a constant-voltage (V=-40 mV) surface of electrical waves (action potentials) propagating inside a 4 cm X 4 cm X 1 cm piece of ventricular heart tissue, evolving according to a quantitatively accurate cardiac model known as the Luo-Rudy 1 model; a realistic anisotropy that rotates with depth has been included. The color indicates position of the surface within the domain. Since muscle tissue contracts shortly after an electrical wave front sweeps through it, the irregular geometry of these waves helps to explain why fibrillating heart muscle can not contract coherently to pump blood.