Giant Fluctuations of Coulomb Drag

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• Dr Adam Price, Quantum Systems and Nanomaterials Group, School of Physics, University of Exeter
• Monday 07 February 2011, 14:15-16:00
• Mott Seminar Room, Cavendish Laboratory, Department of Physics.

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In a system where two parallel conducting layers are located in close proximity to each other, an effect called Coulomb drag can be observed. This Coulomb drag is a direct manifestation of electron-electron interactions, where momentum is transferred from electrons in a current-carrying ‘active’ layer to electrons in the ‘passive’ layer. The drag resistance is a measure of the strength of this effect, and has been used extensively as a sensitive probe of the electron-electron interactions.

More recently it was predicted that at low temperatures mesoscopic fluctuations in the drag resistance would occur, similar to those seen in conventional single-layer systems [1,2]. However, it was shown that in contrast to conventional systems, the fluctuations in the Coulomb drag could exceed the average value, resulting in a negative drag resistance.

I will discuss our measurements of these mesoscopic fluctuations of the Coulomb drag, in which we confirmed the presence of a negative drag resistance for certain values of carrier-density and perpendicular magnetic field. Furthermore, we observed an unanticipated enhancement of these fluctuations, which we ascribed to the important contribution from fluctuations in the local density of states [3,4] in our samples.

References: [1] B. N. Narozhny and I. L. Aleiner, Phys. Rev. Lett. 84, 5383 (2000). [2] B. N. Narozhny, I. L. Aleiner, A. Stern, Phys. Rev. Lett. 86, 3610 (2001). [3] A. S. Price, A. K. Savchenko, B. N. Narozhny, G. Allison, D. A. Ritchie, Science 316, 99 (2007). [4] A. S. Price, A. K. Savchenko, D. A. Ritchie, Phys. Rev. B 81 , 193303 (2010).

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