Disordered Route to the Coulomb Quantum Spin Liquid: Random Transverse   Fields on Spin Ice in Pr$_2$Zr$_2$O$_7$
  Inelastic neutron scattering reveals a broad continuum of excitations in Pr$_2$Zr$_2$O$_7$, the temperature and magnetic field dependence of which indicate a continuous distribution of quenched transverse fields ($\Delta$) acting on the non-Kramers Pr$^{3+}$ crystal field ground state doublets. Spin-ice correlations are apparent within 0.2 meV of the Zeeman energy. A random phase approximation provides an excellent account of the data with a transverse field distribution $\rho(\Delta)\propto (\Delta^2+\Gamma^2)^{-1}$ where $ \Gamma=0.27(1)$ meV. Established during high temperature synthesis due to an underlying structural instability, it appears disorder in Pr$_2$Zr$_2$O$_7$ actually induces a quantum spin liquid. 
J.-J. Wen, S. M. Koohpayeh, K. A. Ross, B. A. Trump, T. M. McQueen, K.   Kimura, S. Nakatsuji, Y. Qiu, D. M. Pajerowski, J. ...
cond-mat.str-el