Deformed Fermi Surface Theory of Magneto-Acoustic Anomaly in Modulated Quantum Hall Systems Near $\nu=1/2$ Hall Systems Near $\nu =1/2$

TL;DR

This paper proposes a deformed composite fermion Fermi surface model to explain anisotropic acoustic anomalies observed near the half-filled Landau level in modulated quantum Hall systems, aligning well with experimental data.

Contribution

It introduces a new generic model of a deformed CF-FS that accounts for anisotropic anomalies in sound velocity and attenuation in modulated quantum Hall systems near ν=1/2.

Findings

Model explains recent acoustic anomalies in experiments.

Calculated conductivity and attenuation match observed magnetic field dependence.

Deformation of CF-FS accounts for anisotropic features.

Abstract

We introduce a new generic model of a deformed Composite Fermion-Fermi Surface (CF-FS) for the Fractional Quantum Hall Effect near $\nu=1/2$ in the presence of a periodic density modulation. Our model permits us to explain the recent surface acoustic wave observations of anisotropic anomalies[R.L Willett et al,PRL vol78,4478 (1997);J.H.Smet et al, PRL vol 80,4538 (1998)] in sound velocity and attenuation--appearance of peaks and anisotropy-- which originate from contributions to the conductivity tensor due to regions of the CF-FS which are flattened by the applied modulation. The calculated magnetic field and wave vector dependence of the CF conductivity, velocity shift, and attenuation agree with experiments.