Investigating field-induced magnetic order in Han purple by neutron scattering up to 25.9 T

The material BaCuSi${}_{2}$O${}_{6}$ has a fascinating dual status as an ancient pigment (the original Terracotta Army was colored with Han purple) and as a quasi-two-dimensional quantum magnet at the modern frontier of research into unconventional quantum many-body phenomena. The HFM/EXED facility at the Helmholtz-Zentrum Berlin neutron source allowed the authors to investigate the field-driven quantum phase transition to magnetic order above 23 T by neutron diffraction and spectroscopy. They report their search for fingerprints of the exotic critical behavior predicted to appear in the two-dimensional regime.