Optical investigations of quantum-dot spin dynamics

TL;DR

This study uses all-optical methods to investigate how various external fields influence spin relaxation mechanisms in single InAs/GaAs quantum dots, revealing the dominant interactions and quantifying hyperfine fields.

Contribution

It provides a detailed analysis of spin relaxation dynamics in quantum dots under different external conditions and quantifies the hyperfine field strength and hole mixing effects.

Findings

Spin relaxation can be tuned by up to five orders of magnitude with external fields.

Hyperfine interaction dominates at low magnetic fields, heavy-light hole mixing at high fields.

Hyperfine (Overhauser) field rms value is approximately 15 mTesla.

Abstract

We have performed all-optical measurements of spin relaxation in single self-assembled InAs/GaAs quantum dots (QD) as a function of static external electric and magnetic fields. To study QD spin dynamics we measure the degree of resonant absorption which results from a competition between optical spin pumping induced by the resonant laser field and spin relaxation induced by reservoirs. Fundamental interactions that determine spin dynamics in QDs are hyperfine coupling to QD nuclear spin ensembles, spin-phonon coupling and exchange-type interactions with a nearby Fermi sea of electrons. We show that the strength of spin relaxation generated by the three fundamental interactions can be changed by up to five orders of magnitude upon varying the applied electric and magnetic fields. We find that the strength of optical spin pumping that we use to study the spin relaxation is determined predominantly by hyperfine-induced mixing of single-electron spin states at low magnetic fields and heavy-light hole mixing at high magnetic fields. Our measurements allow us to determine the rms value of the hyperfine (Overhauser) field to be ~15 mTesla with an electron g-factor of g_e=0.6 and a hole mixing strength of |epsilon|^2 = 0.0005.