Spinons in a new Shastry-Sutherland lattice magnet Pr$_2$Ga$_2$BeO$_7$

TL;DR

This study reports the observation of the largest fermionic spinon thermal conductivity in a new quantum spin liquid candidate Pr$_2$Ga$_2$BeO$_7$ with a Shastry-Sutherland lattice, supported by multiple experimental probes and theoretical analysis.

Contribution

It demonstrates the realization of a quantum spin liquid on the Shastry-Sutherland lattice through the introduction of XY spin anisotropy, a novel finding after decades of research.

Findings

Largest observed $oldsymbol{\kappa_0/T}$ in magnetic oxide QSL candidate

Power-law specific heat and gapless neutron spectra support QSL state

XY spin anisotropy is key to realizing QSL on SSL

Abstract

Identifying the elusive spinon excitations in quantum spin liquid (QSL) materials is what scientists have long sought for. Recently, thermal conductivity ($\kappa$) has emerged to be a decisive probe because the fermionic nature of spinons leads to a characteristic nonzero linear $\kappa_0/T$ term while approaching zero Kelvin. So far, only a few systems have been reported to exhibit such term. Here, we report a $\kappa_0/T \approx$ 0.01 WK$^{-2}$m$^{-1}$, the largest $\kappa_0/T$ value ever observed in magnetic oxide QSL candidates, in a new quantum magnet Pr$_2$Ga$_2$BeO$_7$ with a Shastry-Sutherland lattice (SSL). Its QSL nature is further supported by the power-law temperature dependence of the specific heat, a plateau of muon spin relaxation rate, and gapless inelastic neutron spectra. Our theoretical analysis reveals that the introduction of XY spin anisotropy is the key for Pr$_2$Ga$_2$BeO$_7$ to be the first QSL realized on the SSL, after more than four decades of extensive studies on this celebrated magnetically frustrated lattice.