Quantum spin-glass criticality in disordered frustrated dimer magnets

We study the effect of quenched disorder on non-collinear magnetism in frustrated quantum magnets near quantum criticality. Specifically, we consider a triangular-lattice bilayer Heisenberg model with bond disorder. The clean system has two phases: a dimer quantum paramagnet and a 120° Neel phase, separated by a quantum critical point. Intralayer bond disorder destroys the 120° Neel phase via dipolar textures and results in spin-glass order, such that the system features a quantum phase transition between spin-glass and dimer paramagnetic phases. We study the vicinity of this transition using variant of bond-operator theory and calculate static observables as well as excitation spectra. Bond disorder leads to strong inhomogeneities near the transition and induces real-space localization of excitation modes. In particular, the spin-glass order parameter displays strong quantum fluctuations, indicating the proximity to a spin-liquid-like phase.