Characteristic Bose-Einstein condensation scaling close to a quantum critical point in BaCuSi2O6 -: art. no. 100404

We report an experimental determination of the phase boundary approaching the quantum critical point separating a quantum paramagnetic state and the proposed spin Bose-Einstein condensate of triplons in the spin dimer compound BaCuSi2O6. The ordering temperature is related to the proximity to a quantum critical point at the lower critical magnetic field H-c1=23.52 +/- 0.03 T by a power law parametrized by critical exponent nu. We obtain an experimental estimate of nu=0.63 +/- 0.03 down to a temperature of 0.61 K, which is in good agreement with the mean-field prediction of nu=2/3 for the three-dimensional Bose-Einstein condensation universality class.