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Events on Thursday, August 5th, 2010

R. G. Herb Condensed Matter Seminar
Electrical transport techniques to probe the ground state of closely spaced electron-hole bilayer
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Mike Lilly, Sandia National Laboratory
Abstract: Electron-hole bilayers are expected to make a transition from a pair of weakly coupled two-dimensional systems to a strongly coupled exciton system as the barrier between the layers is reduced. Several clear predictions exist for the transport signature of a transition to an exciton condensate, but recent experiments find a more complicated situation. We report both transport and Coulomb drag measurements electron-hole bilayers fabricated using undoped GaAs/AlGaAs double quantum well heterostructures with gates on the top and bottom of the structure to independently control the electron and hole density. In the drag measurement, current is driven in the electron layer while voltage is measured in the hole layer. Coulomb drag measurements on devices with a 30 nm barrier are consistent with two weakly coupled 2D Fermi systems where the drag decreases with temperature. For a 20 nm barrier, however, we observe an increase in the drag resistance as the temperature is reduced. While these results clearly deviate from Fermi liquid ground states, there are a number of possibilities for the stronger coupling between the layers. This work has been supported by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract No. DE-AC04-94AL85000.
Host: Mark Eriksson
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