Bose Glass Phase in Heisenberg Dimer Systems

We study magnetic-field-induced antiferromagnetic order in cubic dimer systems with bond disorder. In the absence of randomness, their phase diagram features a dimer spin liquid regime at small fields $h < h_{c1}$, an antiferromagnetically ordered phase at intermediate fields $h \in [h_{c1},h_{c2}]$, and a fully polarized regime at large fields beyond $h_{c2}$. Using stochastic series expansion quantum Monte Carlo simulations, the scaling properties at the quantum critical points are shown to be mean-field-like. Furthermore, we demonstrate that in the presence of bond disorder, a new Bose Glass phase separates the dimer spin liquid regime from the antiferromagnetically ordered phase. This resembles strongly the ``triplon localization" which was recently reported for {\rm Tl$_{1-x}$K$_x$CuCl$_3$} where $K$ is randomly substituted for $Tl$.[1] [1] Y. Shindo and H. Tanaka, J. Phys. Soc. Jpn. Vol.{\bf 73} No.10 (2004).