It is demonstrated that the now well-established `flip-flop' mechanism of spin exchange between electrons and nuclei in the quantum Hall effect can be reversed. We use a sample geometry which utilizes separately contacted edge states to establish a local nuclear spin polarization --close to the maximum value achievable-- by driving a current between electron states of different spin orientation. When the externally applied current is switched off, the sample exhibits an output voltage of up to a few tenths of a meV, which decays with a time constant typical for the nuclear spin relaxation. The surprizing fact that a sample with a local nuclear spin polarization can act as a source of energy and that this energy is well above the nuclear Zeeman splitting is explained by a simple model which takes into account the effect of a local Overhauser shift on the edge state reconstruction.
@article{arxiv.cond-mat/0503412,
title = {Electrical read-out of the local nuclear polarization in the quantum Hall effect},
author = {A. Würtz and T. Müller and A. Lorke and D. Reuter and A. D. Wieck},
journal= {arXiv preprint arXiv:cond-mat/0503412},
year = {2009}
}