# Transition from spin-orbit to hyperfine dominated spin relaxation in a cold fluid of dipolar excitons

## TL;DR

This study investigates how spin relaxation mechanisms in dipolar excitons transition from hyperfine to spin-orbit dominance at low temperatures and varying excitation powers, revealing a critical interplay affecting spin lifetime and mobility.

## Contribution

It provides experimental evidence of a transition between hyperfine and spin-orbit dominated spin relaxation in dipolar excitons, linked to temperature, power, and mobility changes.

## Key findings

- Spin lifetime sharply increases below 4.8K.
- Mobility decreases as spin lifetime increases below 4.8K.
- Transition correlates with the emergence of a dark dipolar quantum liquid.

## Abstract

We measure the spin-resolved transport of dipolar excitons in a biased GaAs double quantum well structure. From these measurements we extract both spin lifetime and mobility of the excitons. We find that below a temperature of $4.8$K, there is a sharp increase in the spin lifetime of the excitons, together with a sharp reduction in their mobility. Below a critical power the spin lifetime increases with increasing mobility and density, while above the critical power the opposite trend is observed. We interpret this transition as an evidence of the interplay between two different spin dephasing mechanisms: at low mobility the dephasing is dominated by the hyperfine interaction with the lattice nuclei spins, while at higher mobility the spin-orbit interaction dominates, and a Dyakonov-Perel spin relaxation takes over. The excitation power and temperature regime where the hyperfine interaction induced spin dephasing is observed correlates with the regime where a dark dipolar quantum liquid was reported recently on a similar sample.