Our faculty members are conducting research in the following Experimental Condensed Matter areas:
Humphrey Maris has two research programs. In one program, his group usesfemtosecond optics techniques to generate sound waves in very small structures, such as thin films and wires. These techniques make it possible to study the fundamental physics of very high frequency sound waves in solids (frequency up to 1 THz), and to investigate the flow of heat in thin films and across the interface between films. This work has substantial practical applications in the semiconductor industry and has resulted in the development of new metrologytechniques for use in chip fabrication. A second topic is the study of liquid helium at negative pressures and the investigation of electron bubbles. By applying a negative pressure to the liquid, it is possible to make the electron bubbles explode. In this way it has been possible to make a movie of a single electron.
In superconductivity, Sean Ling's group has longstanding interest in the nature of order-disorder phase transition in vortex matter. The experimental techniques used in the Ling Lab include small angle neutron scattering, acmagnetic susceptibility, calorimetry, etc. In his colloid lab, the focus is in performing controlled experiment using optical tweezers to study the dynamics of defects and defect-driven phase transitions.
Jim Valles' group investigations of correlated electron physics focus on the quantum phases and quantum phase transitions that occur in simple electronic systems such as metal films. They are particularly interested in how the introduction of nano-meter scale structure and disorder can localize electrons and transform a superconductor into a Cooper Pair insulator. These phenomena result from correlations between the conduction electrons that are not included in traditional theories. Their low temperature experiments provide insight into the correlation physics and novel ground states and quantum phase transitions like the superconductor to insulator transition.
Gang Xiao studies electron transport and magnetism in low dimensional systems such as metallic thin films, superlattices, and nanoscaled structures. He directs research toward the understanding of fundamental issues in spintronics, an emerging field that harnesses the electron's spin to create new electronic devices. Some of his research topics include giant and colossal magnetoresistance, spin-dependent magnetic tunneling effects; physics of novelsuperconducting and magnetic nanostructures. Xiao’s group has created ultra-sensitive and ultra-small magnetic tunnel junction sensors for biological and other applications. Pushing to smaller more sensitive devices requires understanding how magnetic materials behave when made with nanometer scale dimensions. His group has developed a method to visualize the flow of electrical current through very small wires. The technique has being applied to the quality control of semiconductor integrated circuits.
General research theme of Vesna Mitrovic's group is the microscopic investigations of matter in the extreme quantum limit of low temperatures and high magnetic fields using the NMR spectroscopy. Many physical phenomena in this limit remain to be understood, such as the possible appearance of fractional spin excitations, quantum phases with complex order parameters, and the coexistence/mixing of several phases. Specifically, Mitrovic's group's research focuses on the study of frustrated quantum magnetism and inhomogeneous superconducting states.
George Seidel's group, in addition to collaborating with Prof. Maris and Prof. Lanou in the development of a superfluid neutrino detector, also studies the magnetic properties of paramagnetic ions in metals at temperatures down to 10mK using SQUID's. The change in magnetization of such systems can be used as sensors with extremely high sensitivity in the calorimetric detection of electromagnetic radiation.
In addition to the condensed matter experimental groups in the Physics Department, several groups in Engineering also have active research programs in condensed matter. Greg Crawford of engineering studies soft condensed matter composites and soft matter materials confined by a surrounding matrix. The surrounding matrix imposes a symmetry breaking, non-planar confinement. The systems under investigations are predominately liquid crystals and polymers, which typically have orientational order but lack the long-range translational order of crystals. Confined liquid crystals deviate from macroscopic bulk liquid crystals because of the large surface-to-volume ratio enabling surface studies to be assessable to integrative experimental methods. Their composite nature profoundly affects the ordering of the liquid crystal molecules and their susceptibility to external fields, making them ideal for a host of new electro-optic applications and intellectually challenging from the basic physics perspective.
Jimmy Xu's laboratory conducts research and explorations on three fronts: quantum electronics, bionanoelectronics, semiconductor lasers, self-organization and collective behavior of correlated electronic and molecular systems, and nanostructures.
Alex Zaslavsky conducts research on devices that could supplement the current silicon transistor-based microelectronics technology. This includes: - devices based on non-classical operating principles, such as quantum mechanical tunneling - devices based on alternative materials, such as germanium-on-insulator and carbon nanotubes - probabilistic error-tolerant silicon device architectures - flexible electronics, such as curved or stretchable electronic displays. The research involves much semiconductor processing, as well as room and low-temperature current transport and magnetotransport measurements.
Arto Nurmikko's research specialty is in experimental semiconductor physics and quantum electronics, particularly on the use of sophisticated laser techniques and advanced spectroscopy for both fundamental and applied purposes. His current interests are focused on optoelectronic material nanostructures and their device science, with one major thrust in semiconductor lasers at blue wavelengths. Other current themes concern the study of ultimate speed limits of magnetization switching by ultrashort laser pulses, and semiconductor/magnetic heterogeneous materials for new ""spintronics"" phenomena and devices.