Quantum Spin Liquids Stabilized by Disorder in Non-Kramers Pyrochlores

TL;DR

This paper demonstrates that quantum spin liquid phases in non-Kramers pyrochlores are robust against disorder, with structural randomness acting as a transverse field, and uses a gauge mean-field theory to analyze stability.

Contribution

It introduces a real-space gauge mean-field approach to exactly include disorder effects in a disordered quantum spin ice model, revealing the phase's stability against disorder.

Findings

Quantum spin ice remains stable up to high disorder levels.

Disorder effects are well captured by an average description in most of the phase diagram.

A Griffiths region appears near the transition to the polarized phase.

Abstract

We investigate the emergence of quantum spin liquid phases in pyrochlore oxides with non-Kramers ions, in which structural randomness 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. We study a minimal model for a disordered quantum spin ice, the transverse-field Ising model, using a real-space formulation of the gauge mean-field theory. This approach allows the inclusion of non-perturbative disorder effects exactly, and thus to assess the stability of the spin-liquid phase with respect to the disorder. 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. A Griffiths region of enhanced disorder-induced fluctuations is restricted to the immediate vicinity of this transition due to the peculiar nature 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.