We present magnetic torque measurements on the Shastry-Sutherland quantum spin system SrCu2(BO3)2 in fields up to 31 T and temperatures down to 50 mK. A new quantum phase is observed in a 1 T field range above the 1/8 plateau, in agreement with recent NMR results. Since the presence of the DM coupling precludes the existence of a true Bose-Einstein condensation and the formation of a supersolid phase in SrCu2(BO3)2, the exact nature of the new phase in the vicinity of the plateau remains to be explained. Comparison between magnetization and torque data reveals a huge contribution of the Dzyaloshinskii-Moriya interaction to the torque response. Finally, our measurements demonstrate the existence of a supercooling due to adiabatic magnetocaloric effects in pulsed field experiments.
@article{arxiv.0712.0926,
title = {Field dependence of the quantum ground state in the Shastry-Sutherland system SrCu$_2$(BO$_3$)$_2$},
author = {F. Levy and I. Sheikin and C. Berthier and M. Horvatic and M. Takigawa and H. Kageyama and T. Waki and Y. Ueda},
journal= {arXiv preprint arXiv:0712.0926},
year = {2008}
}