We experimentally investigate the dielectric response of the low-dimensional gapped quantum magnet Cu2Cl4⋅H8C4SO2 near a magnetic field-induced quantum critical point, which separates the quantum-disordered and helimagnetic ground states. The observed magnetocapacitive effect originates from an improper ferroelectric nature of the transition, which itself is perhaps one of the best known realizations of Bose--Einstein condensation of magnons. Despite that, we find that the magnetocapacitive effect associated with the transition exhibits huge and very unusual anharmonicities.
@article{arxiv.1503.08173,
title = {Giant dielectric nonlinearities at a magnetic Bose-Einstein condensation},
author = {K. Yu. Povarov and A. Reichert and E. Wulf and A. Zheludev},
journal= {arXiv preprint arXiv:1503.08173},
year = {2015}
}