Spinons in a new Shastry-Sutherland lattice magnet Pr₂Ga₂BeO₇

Identifying the elusive spinon excitations in quantum spin liquid (QSL) materials is what scientists have long sought for. Recently, thermal conductivity (κ) has emerged to be a decisive probe because the fermionic nature of spinons leads to a characteristic nonzero linear κ₀/T term while approaching zero Kelvin. So far, only a few systems have been reported to exhibit such term. Here, we report a κ₀/T ≈ 0.01 WK⁻²m⁻¹, the largest κ₀/T value ever observed in magnetic oxide QSL candidates, in a new quantum magnet Pr₂Ga₂BeO₇ 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 Pr₂Ga₂BeO₇ to be the first QSL realized on the SSL, after more than four decades of extensive studies on this celebrated magnetically frustrated lattice.