Role of anisotropy in the spin-dimer compound BaCuSi2O6
  We present results of magnetisation and electron paramagnetic resonance experiments on the spin-dimer system BaCuSi2O6. Evidence indicates that the origin of anisotropic terms in the spin Hamiltonian is from magnetic dipolar interactions. Axial symmetry-breaking is on a very small energy scale of ~11 mK, confirming Bose Einstein condensation critical scaling over an extended temperature range in the vicinity of the quantum critical point. 
Suchitra E. Sebastian, P. Tanedo, P. A. Goddard, S.-C. Lee, A. Wilson,   S. Kim, S. Cox, R. D. McDonald, S. Hill, N. Harriso...