Quantum Spin Liquids Stabilized by Disorder in Non-Kramers Pyrochlores
Abstract
This study investigates the emergence of quantum spin liquid phases in pyrochlore oxides with non-Kramers ions, driven by structural randomness that effectively acts as a transverse field, introducing quantum fluctuations on top of the spin ice manifold. This is contrary to the naive expectation that disorder favors phases with short-range entanglement by adjusting the spins with their local environment. Given this unusual situation, it is essential to assess the stability of the spin-liquid phase with respect to the disorder. To perform this study, a minimal model for disordered quantum spin ice, the transverse-field Ising model, is analyzed using a formulation of gauge mean-field theory (GMFT) directly in real space. This approach allows the inclusion of disorder effects exactly and provides access to non-perturbative effects. The analysis shows that the quantum spin ice remains remarkably stable with respect to disorder up to the transition to the polarized phase at high fields, indicating that it can occur in real materials. Moreover, the Griffiths region of enhanced disorder-induced fluctuations appears tiny and restricted to the immediate vicinity of this transition due to the uniqueness of the low-energy excitations of the problem. For most of the phase diagram, an average description of the disorder captures the physical behavior well, indicating that the inhomogeneous quantum spin ice behaves closely to its homogeneous counterpart.