P-shell carriers assisted dynamic nuclear spin polarization in single quantum dots at zero external magnetic field

TL;DR

This paper reports the first observation of p-shell carrier assisted dynamic nuclear spin polarization in single quantum dots at zero magnetic field, revealing new insights into nuclear spin dynamics and potential control mechanisms.

Contribution

It demonstrates p-shell carriers' role in enhancing nuclear spin polarization in quantum dots, supported by experimental results and numerical simulations, a novel finding in the field.

Findings

Nuclear field increases with p-shell carrier injection

Nuclear spin buildup time abruptly increases when p-shell emission dominates

Numerical simulations support the role of p-shell electrons in nuclear spin dynamics

Abstract

Repeated injection of spin polarized carriers in a quantum dot leads to the polarization of nuclear spins, a process known as dynamic nuclear spin polarization (DNP). Here, we report the first observation of p-shell carrier assisted DNP in single QDs at zero external magnetic field. The nuclear field - measured by using the Overhauser shift of the singly charged exciton state of the QDs - continues to increase, even after the carrier population in the s-shell saturates. This is also accompanied by an abrupt increase in nuclear spin buildup time as p-shell emission overtakes that of the s-shell. We attribute the observation to p-shell electrons strongly altering the nuclear spin dynamics in the QD, supported by numerical simulation results based on a rate equation model of coupling between electron and nuclear spin system. DNP with p-shell carriers could open up avenues for further control to increase the degree of nuclear spin polarization in QDs.