University of Minnesota
School of Physics & Astronomy

Condensed Matter Seminar

Wednesday, April 12th 2017
1:25 pm:
Speaker: Mansour Shayegan, Princeton University
Subject: News from Princeton Flatlands: Probing Exotic Phases of Interacting 2D Systems

In selectively-doped semiconductor structures, the electrons are spatially separated from the dopant atoms to reduce scattering by the ionized impurities. Thanks to the reduced disorder and scattering, such “clean” structures provide nearly ideal 2D systems for studies of electron-electron interaction phenomena, especially at low temperatures and high perpendicular magnetic fields where the thermal and kinetic energies of the electrons are quenched. The dominant electron interaction leads to various fascinating and exotic ground states such as the fractional quantum Hall state, Wigner crystal, and anisotropic (stripe) phases.

In my talk I’ll discuss our latest results in probing the intriguing properties of some of these phases. For example, in high-quality GaAs 2D electrons, a stripe phase is observed in the excited (N = 1) Landau level when a parallel magnetic field (B||) is applied. The stripes are typically oriented perpendicular to the B|| direction. Our experimental data reveals how a periodic density modulation, induced by a surface strain grating from strips of negative electron-beam resist, competes against the B||-induced orientational order of the stripe phase. Even a minute (≪ 1%) imposed density modulation is sufficient to reorient the stripes along the direction of the surface grating, if its period matches the (expected) period of the intrinsic stripes. The data thus suggest that the parallel and perpendicular orientations of the stripes must be energetically very close. I will also present experimental data on other 2D systems, e.g., 2D holes in GaAs or 2D electrons confined to AlAs quantum wells.

Faculty Host: Michael Zudov

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