Anisotropy of quantum Hall phases at filling factor =9/2

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Conference Proceeding

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Strongly correlated electronic systems in the quantum Hall regime start displaying very strong magnetotransport anisotropy at certain low values of the magnetic field below a given critical temperature. The ultimate nature of this emergent anisotropic quantum Hall phase is still elusive despite a decade of studies since their experimental discovery in high mobility GaAs/AlGaAs heterostructures. So far, anisotropy has been observed only in high Landau levels with quantum index n2 and is more pronounced at half-filling of the upper Landau level. Despite the efforts, many questions about the microscopic origin of anisotropy and the physical mechanism of stabilization of anisotropic phases still remain. One way to explain the emergence of anisotropy is to assume that the electrons have formed a unidirectional (or striped) charge density wave state and this path has been followed by many authors. Another scenario consistent with the experimental findings would view the appearance of anisotropy as signature of a phase transition of electrons from an isotropic phase to an anisotropic liquid crystalline phase similar to an isotropic-to-nematic liquid transition. In this work we study the anisotropy of the state with filling factor =9/2 in which the Landau level with index n=2 is half-filled while the lower Landau levels of each spin are full and considered inert thus causing no Landau level mixing. © 2010 American Institute of Physics.

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