The deconfined quantum critical point (DQCP) represents a paradigm shift in quantum matter studies, presenting a "beyond Landau" scenario for order--order transitions. Its experimental realization, however, has remained elusive. Using high-pressure 11B NMR measurements on the quantum magnet SrCu2(BO3)2, we here demonstrate a magnetic-field induced plaquette-singlet to antiferromagnetic transition above 1.8 GPa at a remarkably low temperature, Tc≃0.07 K. First-order signatures of the transition weaken with increasing pressure, and we observe quantum critical scaling at the highest pressure, 2.4 GPa. Supported by model calculations, we suggest that these observations can be explained by a proximate DQCP inducing critical quantum fluctuations and emergent O(3) symmetry of the order parameters. Our findings take the DQCP from a theoretical concept to a concrete experimental platform.
@article{arxiv.2204.08133,
title = {Proximate deconfined quantum critical point in SrCu2(BO3)2},
author = {Yi Cui and Lu Liu and Huihang Lin and Kai-Hsin Wu and Wenshan Hong and Xuefei Liu and Cong Li and Ze Hu and Ning Xi and Shiliang Li and Rong Yu and Anders W. Sandvik and Weiqiang Yu},
journal= {arXiv preprint arXiv:2204.08133},
year = {2023}
}