RESEARCH GROUPS
Condensed Matter Experiment Home Pages
Condensed Matter NMR Spectroscopy (Mitrovic)
Condensed Matter Physics and Single Molecule Biophysics (Ling)
Electron Bubble in Liquid Helium (Maris)
Laboratory for Optoelectronics, Nanostructures and Molecular Engineering (Xu)
Low Temperature Detectors (Seidel)
Nanoscale Physics and Devices (Xiao)
Picosecond Ultrasonics (Maris)
Quasi-2D e- Systems and Magnetic Manipulation of Biological Systems (Valles)
Condensed Matter Experiment
The main goal of experimental condensed matter physics is to seek an understanding of the macroscopic behavior of condensed matter from their microscopic interactions and symmetries through experiments. The fundamental concepts developed in condensed matter physics often have strong impact on other areas of physics. A large group of experimental physicists at Brown study various condensed forms of matter using a wide range of techniques.
Humphrey Maris has two research programs. In one program, his group uses femtosecond 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 metrology techniques 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, ac magnetic 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' investigations of correlated electron physics focus on how nano-meter scale structure affects the quantum mechanical ground state of simple metals. Strongly disrupting the crystalline lattice of a metal or patterning it into nano-meter scale structures can lead to profound changes in its properties. Metals and even superconductors transform into insulators under the right conditions. These alterations involve changes in the correlations between the conduction electrons and thus, cannot be explained using traditional single electron approximation theories. Valles' group's low temperature experiments are leading to insight into the physics that drives these striking changes in the quantum ground states of two dimensional electronic systems.
Gang Xiao studies electron transport and magnetism in low dimensional systems such as metallic thin films, superlattices and ultrafine particles; giant and colossal magnetoresistance effects in layered and oxide solids; spin-dependent magnetic tunneling effects; physics of novel superconducting and magnetic nanostructures; high temperature superconductivity; high vacuum and laser ablation in thin film fabrication.
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.
Selected Recent PhD Dissertations
Alexeandre Anguelouch, "Spin-Polarized Transport and Magnetization Reversal Behavior of Transition Metal and Half Metallic Cr02 Thin Films and Multilayers"
Stefan C. Badescu, "Dynamics of hydrogen atoms absorbed on metallic surfaces"
Brian C. Daly, "Studies of the Thermal Conductivity of Thin Films by Optical Pump and Probe Measurements and Molecular Dynamics Simulations"
Adam K. Fontecchio, "Multiplexing Studies of Holographically-formed Polymer Dispersed Liquid Crystals: Morphology, Structure, and Device Applications"
Antonio C.C. Guimaraes Jr., "Cosmological Information from Weak Gravitational Lensing"
Pavel Kossyrev, "Tailored Molecular Order in Reactive Mesogens"
Jun Liu, "Strain-induced quantization in Si/SiGe Vertical Quantum Dots and Rings"
Alexandros Pertsinidis, "Experimental Studies of Two-Dimensional Colloidal Crystals: Defects, Pinning and Driven Dynamics"
Jun Qi, "Holographic Polymer-Dispersed Liquids Crystals: Physics and Applications"
Benaiah D. Schrag, "Scanning Magnetoresistive Microscopy and Spintronics-based Sensing"
