Single-beam resonant spin amplification of electrons interacting with nuclei in a GaAs/(Al,Ga)As quantum well

TL;DR

This study demonstrates a single-beam resonant spin amplification technique in GaAs/(Al,Ga)As quantum wells, revealing temperature-dependent nuclear spin polarization dynamics and electron g-factor anisotropy through optical and magnetic resonance measurements.

Contribution

It introduces a novel single-beam method for resonant spin amplification, enabling direct observation of nuclear polarization effects in quantum wells.

Findings

Nuclear spin polarization time $T_1$ decreases at lower temperatures.

Resonant spin amplification peaks shift due to nuclear field buildup.

Estimated electron g-factor ratio $g_{ot}/g_{\parallel}=1.3$.

Abstract

The dynamic polarization of nuclear spins interacting with resident electrons under resonant excitation of trions is studied in a nominally undoped GaAs/(Al,Ga)As quantum well. Unlike in common time-resolved pump-probe techniques, we used a single beam approach where the excitation light is modulated between the circular and linear polarization states. The time-integrated intensity of the excitation laser reflected from the sample surface, proportional to the optical generation rate and changes due to the pumping of the resident electrons, is detected. Polarized electrons on the other hand transfer their spin to the lattice nuclei via the hyperfine interaction. Exciting the sample with a train of pulses in an external magnetic field leads to resonant spin amplification observed when the Larmor precession frequency is synchronized with the laser pulse repetition rate. Build-up of the nuclear spin polarization causes a shifting of the RSA peaks since the resulting nuclear field alters the strength of the external magnetic field experienced by the electrons. It was established that the nuclear spin polarization time $T_1$ is temperature dependent and owing to the electron localization at lower temperatures becomes shorter. "Locking" of the nuclear field manifested as the limited by the strength of the external field growth of the nuclear field, that is related to the anisotropy of the electron $g$-factor, was observed. The $g$-factor ratio between the in plane $g_{\parallel}$ and out-of-plane $g_{\bot}$ components was estimated to be $g_{\bot}/g_{\parallel}=1.3$.