Electrically tunable dynamic nuclear spin polarization in GaAs quantum dots at zero magnetic field

TL;DR

This paper demonstrates electrically tunable dynamic nuclear polarization in GaAs quantum dots at zero magnetic field, revealing control over nuclear spin states via bias voltage without changing optical polarization.

Contribution

It introduces a method to control nuclear spin polarization amplitude and sign in GaAs quantum dots using bias voltage at zero magnetic field, highlighting a new electrical tuning mechanism.

Findings

DNP achieved at zero magnetic field in GaAs quantum dots.

Bias voltage variation controls the amplitude and sign of nuclear polarization.

DNP occurs within tens of picoseconds during the exciton lifetime.

Abstract

In III-V semiconductor nano-structures the electron and nuclear spin dynamics are strongly coupled. Both spin systems can be controlled optically. The nuclear spin dynamics is widely studied, but little is known about the initialization mechanisms. Here we investigate optical pumping of carrier and nuclear spins in charge tunable GaAs dots grown on 111A substrates. We demonstrate dynamic nuclear polarization (DNP) at zero magnetic field in a single quantum dot for the positively charged exciton X$^+$ state transition. We tune the DNP in both amplitude and sign by variation of an applied bias voltage V$_g$. Variation of $\Delta$V$_g$ of the order of 100 mV changes the Overhauser splitting (nuclear spin polarization) from -30 $\mu$eV (-22 %) to +10 $\mu$eV (+7 %), although the X$^+$ photoluminescence polarization does not change sign over this voltage range. This indicates that absorption in the structure and energy relaxation towards the X$^+$ ground state might provide favourable scenarios for efficient electron-nuclear spin flip-flops, generating DNP during the first tens of ps of the X$^+$ lifetime which is of the order of hundreds of ps. Voltage control of DNP is further confirmed in Hanle experiments.