Field dependence of the quantum ground state in the Shastry-Sutherland system SrCu$_2$(BO$_3$)$_2$

Florence Lévy-Bertrand (1) , I. Sheikin (1) , C. Berthier (1) , M. Horvatic (1) , M. Takigawa (2) , H. Kageyama (3) , T. Waki (2) , Y. Ueda (2)

1 LCMI-GHMFL - Laboratoire des champs magnétiques intenses
2 ISSP - Institute for Solid State Physics [Tokyo]
3 Department of Chemistry, Kyoto University

We present magnetic torque measurements on the Shastry-Sutherland quantum spin system SrCu$_2$(BO$_3$)$_2$ 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 SrCu$_2$(BO$_3$)$_2$, 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.

Mots clés: adiabatic magnetocaloric effects

Mots clés: Quantum spin system; SrCu$_2$(BO$_3$)$_2$; magnetization plateaus; torque measurement; magnetization measurement; supersolid; adiabatic magnetocaloric effects.

Domaines: Electrons fortement corrélés [cond-mat.str-el]

Florence Lévy-Bertrand, I. Sheikin, C. Berthier, M. Horvatic, M. Takigawa, et al.. Field dependence of the quantum ground state in the Shastry-Sutherland system SrCu$_2$(BO$_3$)$_2$. EPL - Europhysics Letters, 2008, 81, pp.67004. ⟨10.1209/0295-5075/81/67004⟩. ⟨hal-00194333⟩