Field-Induced Bose-Einstein Condensation of Triplons up to 8 K in Sr3Cr2O8

Single crystals of the spin dimer system Sr3Cr2O8 have been grown for the first time. Magnetization, heat capacity, and magnetocaloric effect data up to 65 T reveal magnetic order between applied fields of H-c1 similar to 30.4 T and H-c2 similar to 62 T. This field-induced order persists up to T-c(max)similar to 8 K at H similar to 44 T, the highest observed in any quantum magnet where H-c2 is experimentally accessible. We fit the temperature-field phase diagram boundary close to H-c1 using the expression T-c=A(H-H-c1)(nu). The exponent nu=0.65(2), obtained at temperatures much smaller than T-c(max), is that of the 3D Bose-Einstein condensate (BEC) universality class. This finding strongly suggests that Sr3Cr2O8 is a new realization of a triplon BEC where the universal regimes corresponding to both H-c1 and H-c2 are accessible at He-4 temperatures.