Even-denominator Fractional Quantum Hall Effect at a Landau Level Crossing

TL;DR

This paper reports the discovery of an even-denominator fractional quantum Hall effect at filling factor 1/2, induced by a Landau level crossing in high-mobility GaAs 2D hole systems, revealing new many-body quantum states.

Contribution

It demonstrates an unusual Landau level crossing leading to an even-denominator FQHE at ν=1/2 in 2D hole systems, a phenomenon rarely observed.

Findings

Observation of an even-denominator FQHE at ν=1/2

Landau level crossing in 2D GaAs hole systems

Weakening or destruction of FQHE near LL crossings

Abstract

The fractional quantum Hall effect (FQHE), observed in two-dimensional (2D) charged particles at high magnetic fields, is one of the most fascinating, macroscopic manifestations of a many-body state stabilized by the strong Coulomb interaction. It occurs when the filling factor ($\nu$) of the quantized Landau levels (LLs) is a fraction which, with very few exceptions, has an odd denominator. In 2D systems with additional degrees of freedom it is possible to cause a crossing of the LLs at the Fermi level. At and near these crossings, the FQHE states are often weakened or destroyed. Here we report the observation of an unusual crossing of the two \emph{lowest-energy} LLs in high-mobility GaAs 2D $hole$ systems which brings to life a new \emph{even-denominator} FQHE at $\nu=1/2$.