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Events at Physics

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Events During the Week of August 1st through August 8th, 2010

Monday, August 2nd, 2010

No events scheduled

Tuesday, August 3rd, 2010

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Wednesday, August 4th, 2010

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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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Friday, August 6th, 2010

R. G. Herb Condensed Matter Seminar
Silicon enhancement mode nanostructures for few electron spin devices
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Malcolm Carroll, Sandia National Laboratory
Abstract: Promising coherent control of single electron spins in modulation doped, depletion mode, GaAs quantum dots has been demonstrated [1] with spin decoherence times order of 30 ms with Hahn echo [2]. Spin decoherence times orders of magnitude longer, > 0.6 seconds, have been measured in ensemble spin measurements in silicon but have not yet been realized in single spin silicon nanostructures although numerous groups are showing rapid progress towards this goal. Achieving single electron spin control with long decoherence times will likely require low charge and magnetic disordered silicon devices. This has represented a long standing challenge to the community resulting in the examination of numerous materials, device design and process integration approaches. This talk will describe a silicon metal oxide semiconductor (MOS), open-lateral gated design that produces a confined potential for electrons at the SiO2/Si interface that allows sufficient tunability to both form well behaved double quantum dots (DQD) and overcome some electrostatic non-uniformity in the nanostructure. This structure further provides the ability to implant the quantum dot structures with impurities (Sb), which provides an alternate path to obtaining single electron potentials that can couple and be manipulated by the DQD structure. Electrical transport of both low disorder MOS quantum dots and impurity implant induced resonances will be presented. Modeling of the electrostatics and the excited state spectroscopy of these systems is used to begin to clarify the source of the single electron transport. The effects of processing induced defects and background impurities in the metal oxide semiconductor (MOS) system on electrostatic and magnetic effects on the qubit will also be discussed if time permits.

We wish to acknowledge the research funding support provided by the laboratory directed research and development (LDRD) program at Sandia National Laboratories. Sandia National Labs is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

[1] J. Petta et al., Science 309, 2180 (2005)
[2] H. Bluhm et al., arXiv: 1005.2995 (2010)
Host: Mark Eriksson
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