Download mse seminar - Virginia Tech

MSE SEMINAR
February 20, 2009
113 McBryde Hall
3:30 – 4:30
Refreshments at 3:00
Dr. Jean J. Heremans
Department of Physics
Virginia Tech
“Spin and Quantum-coherent Electron
Transport in Semiconductors”
ABSTRACT
Spin-dependent electronic properties in semiconductor structures may be utilized toward the design of novel
spintronics implementations, and also form a starting point to explore captivating physical phenomena. In particular,
spin-orbit interaction in semiconductor heterostructures and thin films can lead to spin-dependent electron transport
effects, without the presence of magnetic materials. At mesoscopic dimensions, on length scales shorter than the
electron mean free path, the effects of spin-orbit interaction are not averaged out over the geometry. Spin-orbit
interaction then results in observable electronic properties, which lead to interesting device properties as well as
intriguing physics. We pattern mesoscopic geometries on InSb/InAlSb and InAs/AlGaSb or InAs/GaSb
heterostructures, where spin-orbit interaction is strong. We experimentally demonstrate ballistic and quantum-coherent
spin-dependent phenomena, such as spin-split ballistic transport using specialized transverse magnetic focusing
geometries, the creation of fully spin-polarized electron beams using spin-dependent reflection, and quantummechanical interference effects using mesoscopic ring arrays. The spin degree of freedom sometimes results in
surprising effects on quantum-mechanical particle interference phenomena, through the Aharonov-Bohm phase and its
less-explored electromagnetic dual, the Aharonov-Casher phase. Further, we investigate the spin coherence times in
InSb thin films by anti-localization magnetoresistance measurements. Anti-localization is a consequence of particle
interference under spin-orbit interaction, and carries information about both the spin and the phase coherence times of
electrons. Measurements show that in InSb the spin coherence time can reach 70 ps at low temperatures, and that
Elliott-Yafet momentum scattering here dominates spin decoherence.
BIOSKETCH
Dr. Jean Heremans is an associate professor in the Department of Physics at Virginia Tech. Dr. Heremans received a
B.S. and M.S. in Applied Sciences at the University of Leuven (Belgium), and his Ph.D. in 1994 from Princeton
University. He was a postdoctoral fellow at the National High Magnetic Field Laboratory and Florida State University
in Tallahassee, FL, and worked at the semiconductor company Emcore as research scientist. Subsequently he joined
Ohio University as assistant professor and then associate professor and Director of the Nanoscale and Quantum
Phenomena Institute at Ohio University. He moved to Virginia Tech in 2005. Dr. Heremans’ current research interests
include phenomena in condensed matter at high magnetic fields and low temperatures, quantum transport and spindependent phenomena, nanoscale semiconductor structures, magnetic phenomena in reduced dimensions, organic
semiconductors and molecular electronics.