Anomalous Carrier Lifetime Enhancement and Effective Mass Discontinuity Observed during Magnetic-field-induced Subband Depopulation in a Parabolic Quantum Well

TL;DR

This study investigates how magnetic fields influence carrier properties in GaAs/AlGaAs quantum wells, revealing a significant effective mass difference between subbands and an unexpected lifetime enhancement during subband depopulation.

Contribution

It demonstrates the first observation of effective mass discontinuity and lifetime enhancement during magnetic-field-induced subband depopulation in parabolic quantum wells.

Findings

Carrier effective mass differs by 50% between subbands near the threshold.

Second subband lifetime is enhanced near the depopulation threshold.

Two subband transport increases resistance despite lifetime enhancement.

Abstract

In GaAs/AlGaAs parabolic quantum wells, subbands are depopulated by a magnetic field in the well plane. A small additional perpendicular field induces Shubnikov-de-Haas (SdH) oscillations which we have used to determine the carrier density, effective mass, and lifetime, thoughout the two subband to one subband transition. The masses of carriers in the first and second subbands differ by 50% near the threshold of population of the second subband. The second subband SdH lifetime is enhanced near the threshold, even though the onset of two subband transport increases the sample resistance.