Quantum Spin Liquids in Pyrochlore Magnets With Non-Kramers Local Moments

TL;DR

This paper investigates possible quantum spin liquid states in pyrochlore magnets with non-Kramers moments, using theoretical modeling to match experimental neutron scattering data and identify distinct QSL phases.

Contribution

The study applies Schwinger boson mean-field theory and symmetry classification to identify four candidate $ ext{Z}_2$ QSLs consistent with experiments, highlighting two robust phases with dominant transverse exchange.

Findings

Identified four $ ext{Z}_2$ QSLs compatible with neutron data.

Two QSLs are stable with dominant transverse exchange.

Computed spin structure factors to guide experimental distinction.

Abstract

Numerous experiments on pyrochlore oxides Pr$_2$(Zr, Sn, Hf, Ir)$_2$O$_7$ with non-Kramers Pr$^{3+}$ ions suggest that they support a quantum spin liquid (QSL) ground state, but the precise nature of the QSL remains unclear. Quantum spin ice with dominant dipolar Ising and smaller quadrupolar transverse exchange interactions is one such candidate, but a dominant inelastic neutron scattering signal suggests that such a picture may not be consistent with experimental results. The microscopic exchange couplings of these compounds are also not known, leaving room for many possible QSL states. In this work, we use Schwinger boson mean-field theory supplemented by a projective symmetry group classification to study possible $\mathbb{Z}_2$ QSLs in pyrochlore magnets with dipolar-quadrupolar non-Kramers local moments. We build a mean-field phase diagram and find four QSLs in the frustrated region of parameter space that are consistent with inelastic signals observed in neutron scattering data on Pr$_2$Zr$_2$O$_7$ and Pr$_2$Hf$_2$O$_7$. Among these, two robust QSLs occur in the regime with dominant transverse exchange rather than Ising exchange. We then compute the static and dynamic spin structure factors for these QSL candidates, which can be used to distinguish them in neutron scattering experiments.