Quantum spin ice on the breathing pyrochlore lattice

TL;DR

This paper investigates the stability and properties of quantum spin liquids on breathing pyrochlore lattices, revealing a finite parameter space for the phase and broader finite-temperature regimes, with implications for experiments.

Contribution

It introduces a theoretical analysis of quantum spin ice on breathing pyrochlore lattices, showing the existence and stability of quantum spin liquid phases and phase transitions.

Findings

Quantum spin liquid exists in a finite parameter region.

A direct transition occurs between quantum spin liquid and paramagnets.

Breathing pyrochlores exhibit broader finite-temperature spin liquid regimes.

Abstract

The Coulombic quantum spin liquid in quantum spin ice is an exotic quantum phase of matter that emerges on the pyrochlore lattice and is currently actively searched for. Motivated by recent experiments on the Yb-based breathing pyrochlore material Ba$_3$Yb$_2$Zn$_5$O$_{11}$, we theoretically study the phase diagram and magnetic properties of the relevant spin model. The latter takes the form of a quantum spin ice Hamiltonian on a breathing pyrochlore lattice, and we analyze the stability of the quantum spin liquid phase in the absence of the inversion symmetry which the lattice breaks explicitly at lattice sites. Using a gauge mean-field approach, we show that the quantum spin liquid occupies a finite region in parameter space. Moreover, there exists a direct quantum phase transition between the quantum spin liquid phase and featureless paramagnets, even though none of theses phases break any symmetry. At nonzero temperature, we show that breathing pyrochlores provide a much broader finite temperature spin liquid regime than their regular counterparts. We discuss the implications of the results for current experiments and make predictions for future experiments on breathing pyrochlores.