# Giant hyperfine interaction between a dark exciton condensate and nuclei

## TL;DR

The paper shows that a dark exciton condensate in quantum wells causes a strong interaction with nuclei, leading to long-lasting nuclear polarization.

## Contribution

The study reveals a two-orders-of-magnitude enhancement in hyperfine interaction due to the collective nature of the exciton condensate.

## Key findings

- Nuclear polarization spreads across the entire mesa area and lasts for seconds after excitation.
- Hyperfine interaction between nuclear and electron spins is amplified by a factor of N in the condensate.
- The enhancement is attributed to the collective behavior of the N-exciton condensate.

## Abstract

We study the interaction of a dark exciton Bose-Einstein condensate with the nuclei in gallium arsenide/aluminum gallium arsenide coupled quantum wells and find clear evidence for nuclear polarization buildup that accompanies the appearance of the condensate. We show that the nuclei are polarized throughout the mesa area, extending to regions that are far away from the photoexcitation area and persisting for seconds after the excitation is switched off. Photoluminescence measurements in the presence of radio frequency radiation reveal that the hyperfine interaction between the nuclear and electron spins is enhanced by two orders of magnitude. We suggest that this large enhancement manifests the collective nature of the N-exciton condensate, which amplifies the interaction by a factor of N.

The electron-nucleus hyperfine interaction is shown to be strongly enhanced in an exciton condensate.