Density dependence of valley polarization energy for composite fermions

TL;DR

This study investigates how the energy required to fully valley polarize composite fermions in wide AlAs quantum wells varies with electron density, revealing an unexpected trend contrary to existing theories.

Contribution

It provides the first systematic measurement of valley polarization energy of composite fermions as a function of electron density in AlAs quantum wells.

Findings

Valley polarization energy decreases with decreasing density.

Results show good agreement with existing theory overall.

An unexpected trend in valley polarization energy was observed.

Abstract

In two-dimensional electron systems confined to wide AlAs quantum wells, composite fermions around the filling factor $\nu$ = 3/2 are fully spin polarized but possess a valley degree of freedom. Here we measure the energy needed to completely valley polarize these composite fermions as a function of electron density. Comparing our results to the existing theory, we find overall good quantitative agreement, but there is an unexpected trend: The measured composite fermion valley polarization energy, normalized to the Coulomb energy, decreases with decreasing density.