Field-induced Bose-Einstein condensation of a strongly correlated spin liquid in BaCuSi2O6

Low-temperature specific heat and magnetization experiments were performed in single-crystal samples of BaCuSi2O6 at high magnetic fields. These properties show changes upon entering a roughly parabolic region of the (H,T) phase diagram defined by critical magnetic fields Hc1=23.5T and Hc2=49T, and a critical temperature Tc=3.78K. The specific heat measured at 37T shows a λ-shaped anomaly, and the magnetic susceptibility drops sharply on cooling. We used analytical methods and a directed-loop Monte Carlo algorithm to reproduce the experimental results, which are consistent with Bose-Einstein condensation of strongly correlated spin degrees of freedom