Thermopower of Two-Dimensional Electrons at $\nu$ = 3/2 and 5/2

TL;DR

This study measures the thermopower of high-mobility two-dimensional electrons at different filling factors, revealing insights into electron diffusion, composite fermion mass, and the energy gap of the fractional quantum Hall state at ν=5/2.

Contribution

It provides the first detailed thermopower measurements at ν=3/2 and ν=5/2, linking thermopower behavior to composite fermion properties and quasiparticle statistics.

Findings

Thermopower at zero field is dominated by electron diffusion below 150 mK.

At ν=3/2, thermopower allows estimation of composite fermion effective mass.

At ν=5/2, thermopower indicates the presence of an energy gap and exceeds predictions based on non-abelian quasiparticle entropy.

Abstract

The longitudinal thermopower of ultra-high mobility two-dimensional electrons has been measured at both zero magnetic field and at high fields in the compressible metallic state at filling factor $\nu = 3/2$ and the incompressible fractional quantized Hall state at $\nu = 5/2$. At zero field our results demonstrate that the thermopower is dominated by electron diffusion for temperatures below about $T = 150$ mK. A diffusion dominated thermopower is also observed at $\nu = 3/2$ and allows us to extract an estimate of the composite fermion effective mass. At $\nu = 5/2$ both the temperature and magnetic field dependence of the observed thermopower clearly signal the presence of the energy gap of this fractional quantized Hall state. We find that the thermopower in the vicinity of $\nu = 5/2$ exceeds that recently predicted under the assumption that the entropy of the 2D system is dominated by non-abelian quasiparticle exchange statistics.