University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Colloquium

Thursday, April 13th 2017
3:35 pm:
Speaker: Mansour Shayegan, Princeton
Subject: Measurements of Composite Fermion Geometric Resonance
Refreshments to be served outside Smith 100 after the colloquium.

There has been a surge of recent interest in the physics of interacting, two-dimensional (2D) electrons in a large perpendicular magnetic field when they occupy a half-filled Landau level. The long ago proposed composite fermion (CF) picture, in which two magnetic flux quanta are bound to each electron to form a CF, explains many properties of the system. These include the compressible (metallic) behavior of the 2D system at filling factor ν = ½, the existence of a Fermi contour with a well-defined Fermi wave vector, and the presence of fractional quantum Hall states as the filling deviates from ν = ½. In this talk, I will highlight the results of several recent experiments that probe the presence and properties of CFs via measuring the geometric resonance of CFs’ cyclotron orbit diameter with the period of an imposed, unidirectional density modulation. The data reveal several important aspects: (1) An unexpected asymmetry of the CFs’ Fermi wave vector for filling factors smaller and larger than ν = ½, suggesting a subtle breaking of particle-hole symmetry. (2) Anisotropic Fermi contours for CFs that can be tuned by applying in-plane magnetic field or in-plane strain. The strain results are particularly intriguing as they imply that the CFs inherit a Fermi contour anisotropy from their (parent) zero-field particles through a simple relation. (3) I will also discuss a bilayer experiment where the geometric resonance of CFs in one layer is used to probe an electron Wigner solid in the other layer.

Faculty Host: Michael Zudov

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