Persistent Spin Helix Manipulation by Optical Doping of a CdTe Quantum Well

TL;DR

This study demonstrates how optical doping can manipulate the persistent spin helix in a CdTe quantum well, revealing tunable spin dynamics and validating a kinetic theory model through experimental and theoretical analysis.

Contribution

It introduces a method to control the persistent spin helix in a II-VI compound using optical doping, supported by experimental validation and kinetic theory modeling.

Findings

Optical doping influences spin diffusion dynamics.

Spin-orbit coupling parameters are independently extracted.

Spatiotemporal precession patterns are observed and modeled.

Abstract

Time-resolved Kerr-rotation microscopy explores the influence of optical doping on the persistent spin helix in a [001]-grown CdTe quantum well at cryogenic temperatures. Electron spin diffusion dynamics reveal a momentum-dependent effective magnetic field providing SU(2) spin-rotation symmetry, consistent with kinetic theory. The Dresselhaus and Rashba spin-orbit coupling parameters are extracted independently from rotating the spin helix with external magnetic fields applied parallel and perpendicular to the effective magnetic field. Most importantly, a non-uniform spatiotemporal precession pattern is observed. The kinetic theory framework of spin diffusion allows for modeling of this finding by incorporating the photocarrier density into the Rashba ($\alpha$) and the Dresselhaus ($\beta_3$) parameters. Corresponding calculations are further validated by an excitation-density dependent measurement. This work shows universality of the persistent spin helix by its observation in a II-VI compound and the ability to fine-tune it by optical doping.