Field-induced criticality in a gapped quantum magnet with bond disorder
  Neutron diffraction and calorimetric measurements are used to study the field-induced quantum phase transition in piperazinium-Cu$_2$(Cl$_{1-x}$Br$_x$)$_6$ ($x=0$, x=3.5% and x=7.5%), a prototypical quantum antiferromagnet with random bonds. The critical indexes $\phi$ and $\beta$ are determined. The findings contradict some original predictions for Bose Glass based on the assumption $z=d$, but are consistent with recent theoretical results implying $z<d$. Inelastic neutron experiments reveal that disorder has a profound effect on the lowest-energy magnetic gap excitation in the system. 
D. H\"uvonen, S. Zhao, M. M{\aa}nsson, T. Yankova, E. Ressouche, C.   Niedermayer, M. Laver, S. N. Gvasaliya, A. Zheludev
cond-mat.str-el