Magnetic field dependence of the electron spin revival amplitude in periodically pulsed quantum dots

TL;DR

This study investigates how external magnetic fields influence electron spin revival amplitudes in periodically pulsed quantum dots, combining experimental data with two advanced theoretical models to explain the nuclear Zeeman effect's role.

Contribution

It introduces two complementary simulation approaches capable of modeling spin dynamics over extensive timescales and explains the magnetic field dependence of revival amplitudes in quantum dots.

Findings

Revival amplitude shows a nonmonotonic dependence on magnetic field.

Both models reproduce a minimum at 4 T due to nuclear Zeeman effect.

Nuclear Larmor precession influences electron spin dynamics.

Abstract

Periodic laser pulsing of singly charged semiconductor quantum dots in an external magnetic field leads to a synchronization of the spin dynamics with the optical excitation. The pumped electron spins partially rephase prior to each laser pulse, causing a revival of electron spin polarization with its maximum at the incidence time of a laser pulse. The amplitude of this revival is amplified by the frequency focusing of the surrounding nuclear spins. Two complementary theoretical approaches for simulating up to 20 million laser pulses are developed and employed that are able to bridge between 11 orders of magnitude in time: a fully quantum mechanical description limited to small nuclear bath sizes and a technique based on the classical equations of motion applicable for a large number of nuclear spins. We present experimental data of the nonmonotonic revival amplitude as function of the magnetic field applied perpendicular to the optical axis. The dependence of the revival amplitude on the external field with a profound minimum at $4\;$T is reproduced by both of our theoretical approaches and is ascribed to the nuclear Zeeman effect. Since the nuclear Larmor precession determines the electronic resonance condition, it also defines the number of electron spin revolutions between pump pulses, the orientation of the electron spin at the incidence time of a pump pulse, and the resulting revival amplitude. The magnetic field of $4\;$T, for example, corresponds to half a revolution of nuclear spins between two laser pulses.