Decay and revival of electron spin polarization in an ensemble of (In,Ga)As quantum dots

TL;DR

This study investigates how periodic optical excitation influences electron spin polarization and nuclear spin interactions in (In,Ga)As quantum dots, revealing nuclear effects on spin dynamics and mode formation.

Contribution

It introduces a pulse protocol to analyze spin precession modes and extends a nuclear polarization model to include optically detuned quantum dots.

Findings

Long-living nuclear polarization accelerates electron spin buildup.

Nuclear polarization induces additional electron spin precession modes.

Nuclear effects significantly influence spin dynamics in quantum dots.

Abstract

The periodic optical orientation of electron spins in (In,Ga)As/GaAs quantum dots leads to the formation of electron spin precession modes about an external magnetic field which are resonant with the pumping periodicity. As the electron spin is localized within a nuclear spin bath, its polarization imprints onto the spin polarization of the bath. The latter acts back on the electron spin polarization. We implement a pulse protocol where a train of laser pulses is followed by a long, dark gap. It allows us to obtain a high-resolution precession mode spectrum from the free evolution of the electron spin polarization. Additionally, we vary the number of pump pulses in a train to investigate the build-up of the precession modes. To separate out nuclear effects, we suppress the nuclear polarization by using a radio-frequency field. We find that a long-living nuclear spin polarization imprinted by the periodic excitation significantly speeds up the buildup of the electron spin polarization and induces the formation of additional electron spin precession modes. To interpret these findings, we extend an established dynamical nuclear polarization model to take into account optically detuned quantum dots for which nuclear spins activate additional electron spin precession modes.