Composite fermion valley polarization energies: Evidence for particle-hole asymmetry

TL;DR

This paper investigates composite fermions in AlAs, revealing that valley polarization energies differ around filling factors 1/2 and 3/2, providing evidence for particle-hole asymmetry in fractional quantum Hall states.

Contribution

It provides experimental evidence that particle-hole symmetry is broken in composite fermion valley polarization energies in AlAs, contrasting with ideal symmetry expectations.

Findings

Valley polarization energy around ν=1/2 is smaller than around ν=3/2.

Composite fermions possess a valley degree of freedom near ν=1/2 and 3/2.

Particle-hole symmetry is broken in the observed fractional quantum Hall states.

Abstract

In an ideal two-component two-dimensional electron system, particle-hole symmetry dictates that the fractional quantum Hall states around $\nu = 1/2$ are equivalent to those around $\nu = 3/2$. We demonstrate that composite fermions (CFs) around $\nu = 1/2$ in AlAs possess a valley degree of freedom like their counterparts around $\nu = 3/2$. However, focusing on $\nu = 2/3$ and 4/3, we find that the energy needed to completely valley polarize the CFs around $\nu = 1/2$ is considerably smaller than the corresponding value for CFs around $\nu = 3/2$ thus betraying a particle-hole symmetry breaking.