Condensed Matter

Condensed matter physics is one of the most diverse areas of physics, with many practical applications exemplified by those in electronics: microprocessors, memory, display, and magnetic imaging. The condensed matter group at Texas A&M currently conists of eight experimentalists (G. Agnolet, I. F. Lyuksyutov, D. G. Naugle, Igor Roshchin, J. H. Ross, W. Teizer, M. Weimer, W. Wu) and nine theorists (A. Abanov, R. E. Allen, A. Belyanin, A. Finkelstein, C. R. Hu, H. Katzgraber, V. Pokrovsky, W. M. Saslow, J. Sinova). These faculty lead individual research groups, and are also involved in a number of collaborative projects. Additional condensed matter and materials-related research is described under the Applied Physics program description. Many members of the condensed matter group also belong to the interdisciplinary Materials Research Program at Texas A&M.

Major research equipment includes: A pulsed laser deposition facility, superconducting solenoids ranging to 140 kG, four dilution refrigerators for studies down to 0.003K, SQUID and extraction magnetometers, a CTI 1400 helium liquefier, clean high-vacuum thin-film evaporation facility, a surface analysis system (UPS/XPS, SIMS, ISS), a class 100 clean room facility, electron beam lithography capabilities for patterning, UHV scanning tunneling microscope (see image), atomic force microscopy, magnetic force microscopy, and a 9 T solid-state NMR facility.

Prof. Glenn Agnolet's focus is on experimental low-temperature physics. He has studied the universal scaling of the two-dimensional superfluid phase transition of ⁴He films and the effects of impurities on the growth dynamics of the ⁴He solid-liquid interface using crystallization waves. One of his current projects is investigating the potential of a new configuration for inelastic electron tunneling spectroscopy (IETS) and the development of a low temperature scanning probe microscope capable of performing IETS.

Prof. Roland E. Allen has made many contributions in various areas of condensed matter physics. The current emphasis is on the response of biological molecules and materials to light, and on mechanisms for laser control of chemical reactions. The molecules include retinal, chlorophyll, melanin, and 7-dehydrocholesterol. The materials include gallium arsenide, silicon, C60, and molecules on surfaces. The response of matter to ultrafast and ultra-intense laser pulses, which is one of the issues investigated in this work, is a current frontier of physics, chemistry, and biology.

Prof. Chia-Ren Hu's main research interest has been on space- and time-dependent properties of superconductivity and superfluidity, but he has also worked on light scattering and it's symmetry theorems as well as on fractional statistics and anyons. His current research is on anisotropy and pairing-symmetry related properties of high-Tc superconductors, with a strong side interest on quantum optics, and Bose-Einstein condensation of trapped atoms.

Prof. Donald G. Naugle focuses on 1) electron transport and superconductivity in amorphous metals 2) the influence of lattice disorder on electron transport, magnetic ordering and colossal magnetoresistance in perovskite conducting oxides (particularly doped lanthanum manganites) 3) transport, magnetic andsuperconducting properties of new layered compounds (rare-earth-nickel-borocarbides) which exhibit a wide range of unusual phenomena (superconductivity, magnetic ordering, coexistence of superconductivity and magnetism and heavy fermion behavior). Experimental techniques include electron transport (resistivity, thermopower, magnetoresistance, Hall effect, thermal conductivity), electron tunneling, and magnetization and magnetic susceptibility (both SQUID and conventional) measurements. Materials preparation techniques include pulsed laser deposition, ultra high vacuum physical vapor deposition, and rapid quenching by melt-spinning or splat-quenching.

Prof. Valery Pokrovsky is formerly a section head and currently still a Principal Scientist of the world-famous Landau Institute of Theoretical Physics. He and A. Z. Patashinsky shared the 1984 Landau Prize for their work on phase transitions. His research areas include scattering theory, statistical mechanics, two-dimensional systems, magnetism, superconductivity, and the quantum Hall effect. His group is currently working on the quantum behavior of single-molecule nano-scale magnets, and a new class of phenomena based on the strong interaction between magnetic superstructures, either structural (magnetic nano-dots) or topological, and vortices in superconductors.

Prof. Joseph H. Ross, Jr. studies materials physics using NMR spectroscopy, scanning force microscopy (see device and output), and other techniques. His recent work has included design of new magnetic silicon and germanium clathrates and study of the superconducting and magnetic properties of these cage-type materials. The expanded frameworks and loosely-held ions in these materials lead to interesting electronic and vibrational behavior. Further work in his group is focused on hybridization-gap alloys and related intermetallics, and on magnetic properties of new ordered rare-earth alloys. He has also been using computational techniques to study these systems, and he directs the IGERT interdisciplinary graduate curriculum for new computational techniques in materials science.

Prof. Wayne M. Saslow investigates superfluidity (heat flow and thermal healing in ⁴He, the anisotropic hydrodynamic response of ³He, and the properties of superfluid solids), superconductivity, magnetism (anti-ferromagnetism at surfaces, magnetism with random anisotropy and random exchange), and the electro-dynamic response of matter. His present research is directed toward the electrical properties of systems with multiple charge-carriers, including bi-polar semiconductors, voltaic cells, and mixed ionic-electronic conductors. With V. Pokrovsky, research also is being performed on the theory of thin magnetic films.

Prof. Jairo Sinova's group focuses on spintronics and strongly correlated systems. Spintronics is the subfield of condensed matter physics in which the charge and spin degrees of freedom of the electrons are treated in an equal footing to generate novel and unexpected phenomena. His work on semiconductor spintronics, such as the proposal of intrinsic spin-Hall effect and his theory work on diluted magnetic semiconductors, has been highly cited and sprang much interest in the field. Most of his theoretical research is strongly coupled with many experimental efforts and his group collaborates strongly with the University of Nottingham, the Institute of Physics of the Czech Republic, and Wurzburg University. His group uses multiple computational and analytical models of spintronic based materials such as non-equilibriums Green's function techniques, effective Hamiltonian models, exact diagonalization and Monte-Carlo algorithms, mean field calculations and linear response Kubo formalism techniques. His prior work has been on cold atom systems, spin-glasses, organic semiconductors, and the quantum Hall effect.

Prof. Michael B. Weimer and his group focus on developing a comprehensive experimental picture of the structure and electronic properties at III-V semiconductor surfaces and interfaces with scanning tunneling microscopy (STM - see apparatus image and STM image, image). Recent work has taken advantage of the nanometer-scale spatial resolution afforded by STM to advance our understanding of two especially significant problems in III-V epitaxial growth: the precise structure of the interfaces in type-II semiconductor superlattices and quantum wells, and the onset of atomic ordering in III-V semiconductor alloys.