Field dependence of the quantum ground state in the Shastry-Sutherland system SrCu₂(BO₃)₂

¹  Grenoble High Magnetic Field Laboratory (GHMFL), CNRS - BP 166, 38042 Grenoble Cedex 09, France
²  Institute for Solid State Physics, University of Tokyo - Kashiwanoha, Kashiwa, 277-8581, Japan
³  Department of Chemistry, Graduate School of Science, Kyoto University - Kyoto 606-8502, Japan

Received: 30 November 2007
Accepted: 30 January 2008

Abstract

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 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.