Nanosecond-scale magneto-exciton energy oscillations in quantum wells

TL;DR

This paper presents experimental evidence of nanosecond-scale spin memory in quantum wells, showing magnetic-field-induced oscillations of exciton energies due to spin-dependent interactions, with implications for long-lived spin states.

Contribution

It demonstrates long-lived spin coherence in nonradiative excitons in quantum wells, revealing a new mechanism for spin memory based on electron-electron exchange interactions.

Findings

Magnetic-field-induced oscillations of exciton energies observed.

Spin relaxation time of electrons in nonradiative excitons exceeds hole spin relaxation time.

Oscillations persist over nanosecond timescales, much longer than decoherence times.

Abstract

We report on the experimental evidence for a nanosecond time-scale spin memory based on nonradiative excitons. The effect manifests itself in magnetic-field-induced oscillations of the energy of the optically active (radiative) excitons. The oscillations detected by a spectrally-resolved pump-probe technique applied to a GaAs/AlGaAs quantum well structure in a transverse magnetic field persist over a time scale, which is orders of magnitude longer than the characteristic decoherence time in the system. The effect is attributed to the spin-dependent electron-electron exchange interaction of the optically active and inactive excitons. The spin relaxation time of the electrons belonging to nonradiative excitons appears to be much longer than the hole spin relaxation time.