Composite fermions in a wide quantum well in the vicinity of the filling factor 1/2

TL;DR

This study investigates the AC conductance of a wide quantum well near filling factor 1/2, revealing a compressible state of composite fermions and their heating effects, contrasting with the FQHE observed near 3/2.

Contribution

It provides experimental evidence of composite fermion behavior in a wide quantum well near $ u=1/2$, including nonlinear conductance effects due to acoustic wave heating.

Findings

Confirmation of a compressible composite fermion state at $ u=1/2$

Frequency independence of conductance suggests a non-FQHE regime

Nonlinear conductance behavior attributed to acoustic heating of composite fermions

Abstract

Using acoustic method we study dependences of transverse AC conductance, $\sigma (\omega)$, on magnetic field, temperature and the amplitude of AC electric field in a wide (75 nm) quantum well (QW) structure focusing on the vicinity of the filling factor $\nu =1/2$. Measurements are performed in the frequency domain 30-307 MHz and in the temperature domain 20-500 mK. Usually, in wide QW structures closely to $\nu =1/2$ the fractional quantum Hall effect (FQHE) regime is realized at some parameters of the sample. However, in our structure, at $\nu =1/2$ it is a compressible state corresponding to gas of composite fermions which is observed. This is confirmed by apparent frequency independence and weakly decreasing temperature dependence of $\mathrm{Re}\, \sigma(\omega)$. Comparing the dependences of this quantity on temperature and power of the acoustic wave we conclude that the observed nonlinear behavior of the conductance is compatible with heating of the composite fermions by the acoustic wave. For comparison, we also study the vicinity of $\nu = 3/2$ where the FQHE regime is clearly observed.