The Strangely Rapid Diffusion of Electrons in Magnetic and Non-Magnetic Semiconductors

Thursday, October 03, 2013
11:45 AM - 12:55 PM
Lo Schiavo Science 303 - Computational Lab
Event Type
Events and Lectures

 Physics and Astronomy Spring Colloquium Series
Chris Weber (Assistant Professor of Physics, Santa Clara University)
"The Strangely Rapid Diffusion of Electrons in Magnetic and Non-Magnetic Semiconductors"
October 3, 2013, 11:45am-12:55pm, LS 303

Abstract: Ultrafast optical measurements of diffusivity probe material properties of both practical and fundamental importance: diffusion currents of electrons or holes play an important role in the operation of many semiconductor devices, while the Einstein's relation connects a particle's diffusivity to its mobility and its density of states. The magnetic semiconductor (Ga,Mn)As could play an important role in spintronic technology, but still poses vexed questions about the role of charge carriers in its magnetism. The incorporation of magnetic manganese into GaAs introduces significant disorder; nonetheless, our ultrafast measurements show charge carriers diffusing as quickly as they would in pristine GaAs, and show that the conduction-band density of states is unaffected by Mn. These findings may hold clues to the nature of magnetism in (Ga,Mn)As. In a related p-type semiconductor, our measurements of indium phosphide also show rapid diffusion of photoexcited carriers, enhanced markedly by Pauli repulsion as the photoexcited density increases. I will explain why, although this enhancement is in principle expected, prior measurements of p-type semiconductors have always shown the opposite trend.

Bio: Chris Weber received his B.A. and Ph.D. degrees in physics from UC Berkeley, where his studies of spin diffusion in semiconductor quantum wells resulted in the observations of spin Coulomb drag and of the persistent spin helix state. As a postdoc at Lawrence Berkeley National Laboratory, he measured properties of matter at 10,000 Kelvin. Since 2008 he has been an Assistant Professor of Physics at Santa Clara University. His research focuses on ultrafast dynamics of electrons and spin in semiconductors and complex materials.

For more information, please call the Physics Department x6615.


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