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.
@article{arxiv.cond-mat/0606244,
title = {Role of anisotropy in the spin-dimer compound BaCuSi2O6},
author = {Suchitra E. Sebastian and P. Tanedo and P. A. Goddard and S. -C. Lee and A. Wilson and S. Kim and S. Cox and R. D. McDonald and S. Hill and N. Harrison and C. D. Batista and I. R. Fisher},
journal= {arXiv preprint arXiv:cond-mat/0606244},
year = {2011}
}