Valley polarization and susceptibility of composite fermions around nu=3/2

TL;DR

This study investigates the valley polarization of composite fermions in an AlAs quantum well near filling factor 3/2, revealing how strain influences their valley susceptibility and polarization through magnetotransport measurements.

Contribution

It provides the first measurement of CF valley susceptibility and polarization, extending understanding of composite fermions to include valley degrees of freedom.

Findings

CFs exhibit valley polarization behavior similar to spin polarization.

Valley susceptibility can be quantitatively determined from Landau level crossings.

Results align with a simple Landau level fan diagram for CFs.

Abstract

We report magnetotransport measurements of fractional quantum Hall states in an AlAs quantum well around Landau level filling factor nu = 3/2, demonstrating that the quasiparticles are composite Fermions (CFs) with a valley degree of freedom. By monitoring the valley level crossings for these states as a function of applied symmetry-breaking strain, we determine the CF valley susceptibility and polarization. The data can be explained well by a simple Landau level fan diagram for CFs, and are in nearly quantitative agreement with the results reported for CF spin polarization.