Condensed Matter Experiment

The condensed matter experimentalists carry out vigorous efforts across a wide variety of important research areas, ranging from semiconductor organic multilayers to single-electron transistors and semiconductor nanowires. A partial listing follows. Thin organic films, organic multilayers and hybrid organic/inorganic nanosystems are fabricated by organic molecular beam deposition. The purpose of these studies is to improve the microscopic understanding of the exciton dynamics of excitations in organic materials and to combine the properties of the organic and inorganic compounds in a superior way.

In the area of semiconductors, low dimensional semiconductors, in particular, MBE-grown II-VI quantum wells and quantum dots are being investigated using a variety of light scattering techniques including low temperature cw and time-resolved photoluminescence, Raman scattering and degenerate four-wave-mixing. In addition there is extensive research on the electronic and spin properties of semiconductor nanowires and nanowire heterostructures. We combine high-resolution optical spectroscopy with spatial- and temporal-resolution in order to connect the structure of the nanostructures with their physical properties. Far-infrared studies of metal-insulator transition and superconductivity in high Tc cuprates and far-infrared absorption by monodispersed small metal particles such as Au55 clusters are also being pursued.

At very low temperatures (~50 mK) Single-Electron Transistors are used to study the dynamics of Kondo-correlated electrons by advanced microwave-frequency spectroscopic tools. Furthermore the charge and spin transport in semiconducting quantum wires on length scales of 50-500 nm at temperatures down to 25 mK are investigated.

Howard Jackson is doing research in low dimensional semiconductors, in particular quasi one dimensional semiconductor nanowires. Semiconductor nanowires including GaAs, InP, and CdS as well as heterostructures like core/shell nanowires with a GaAs core and GaP shell are being investigated. A variety of light scattering techniques including low temperature photoluminescence, time-resolved photoluminescence, photoluminescence excitation spectroscopy and Raman scattering are being used. Spatially-resolved photocurrent transport measurements are also being used. Most recently a powerful new optical technique, photomodulated Raleigh scattering, has been developed to probe these structures.

Young Kim focuses his research on far-infrared studies of metal-insulator transition and superconductivity in high Tc cuprates and far-infrared absorption by monodispersed small metal particles such as Au55 clusters.

Andrei Kogan uses Single-Electron Transistors—specially fabricated semiconductor devices—to trap small numbers of electrons in regions of space only several tens of nanometers in size and study the dynamic properties of their quantum states. The current projects focus on testing the universal principles predicted to govern the dynamics of Kondo-correlated electrons and developing advanced microwave-frequency spectroscopic tools for studying quantum transport in few--level quantum systems on short time scales. Dr. Kogan's group also uses microwave-frequency measurements to investigate mechanisms via which living cells communicate with each other. The techniques employed by Dr. Kogan's group include state-of-the-art refrigeration, nanoscale device fabrication, low-level transport measurements, numerical simulations of microwave-frequency circuits and precision vector measurements of microwave signals.

David Mast is doing research in fabricating and investigating the transport and thermodynamic properties of three-dimensional arrays of low Tc Josephson junction arrays. Investigating the transport properties of two-dimensional low Tc and high Tc Josephson junction arrays. Developing near-field scanning microwave microscopes and carrying out associated investigation of superconducting, semiconducting and dielectric films and materials. Developing telecommunication filters using single- domain YBCO materials. Pulsed laser deposition of superconducting and semiconducting materials and thin films.

Leigh Smith is doing research which is targeted towards understanding the electronic and spin properties of semiconductor nanostructures, particularly nanowires and nanowire heterostructures. His research group combines high-resolution optical spectroscopy with spatial- and temporal-resolution in order to connect the structure of the nanostructures with their physical properties.

Hans-Peter Wagner is investigating the relaxation dynamics and dephasing of excitons in semiconductor nanostructures (quantum wells and –dots) and in semiconductor nanowires. Ultrafast non-linear optical methods like degenerate four-wave-mixing and heterodyne interferometry are being used for these investigations. Of particular interest is the investigation of a novel phase coherent photorefractive effect which uses the coherence of excitons for time-gating in depth-resolved holographic imaging. Further investigations include thin organic films, organic multilayers and hybrid organic/inorganic nanosystems fabricated by organic molecular beam deposition. A variety of optical methods including low-temperature and time-resolved photoluminescence as well as photoreflectance measurements are being used.