Phonon Absorption at the Magneto-Roton Minimum in the Fractional Quantum Hall Effect

TL;DR

This study presents the first phonon absorption measurements in the fractional quantum Hall regime, revealing that phonon-based energy gap measurements are robust against disorder and align with theoretical predictions.

Contribution

It introduces phonon absorption as a reliable method to measure energy gaps in fractional quantum Hall systems, insensitive to sample disorder.

Findings

Phonon absorption gaps are similar across samples with different mobilities.

Phonon absorption measurements agree with activation gap measurements in high mobility samples.

Results at ν=2/3 match theoretical expectations.

Abstract

We have made the first phonon absorption measurements in the fractional quantum Hall r\'egime. Experiments have been conducted on two samples which have similar electron densities but greatly differing mobilities. The energy gaps as measured by activation studies of the longitudinal resistance differ by a factor of two. Phonon absorption measurements give almost identical values for the energy gap demonstrating that the gap measured in this way is rather insensitive to disorder. The value of this gap is in agreement with the activation gap measured in the high mobility sample. Values obtained at $\nu=2/3$ are in good agreement with theory.