Interplay of disorder and spin liquid physics in the triangular-lattice antiferromagnet YbZn2GaO5

Abstract

YbZn2GaO5 has recently emerged as a structurally ideal triangular-lattice antiferromagnet and a promising candidate for hosting a U(1) Dirac quantum spin-liquid (QSL) ground state. However, signatures of broadened crystal electric field (CEF) excitations have raised questions about potential site disorder and its impact on the intrinsic spin dynamics. In this study, we employ 71Ga nuclear magnetic resonance (NMR) and muon spin relaxation (muSR) to microscopically probe both the structural and magnetic properties of YbZn2GaO5. NMR spectra reveal two inequivalent 71Ga sites and a broad distribution of quadrupolar frequencies, providing clear evidence of Ga$^{3+}$/Zn$^{2+}$ site mixing and local CEF randomness. The NMR spin-lattice relaxation rate exhibits, down to 1.3~K, a power-law temperature dependence, consistent with persisting spin dynamics below the exchange energy scale in a frustrated magnet. Complementary muSR measurements further show that the spin dynamics persist down to 30mK, with no signs of spin freezing. Together, these results establish that YbZn2GaO5 presents substantial structural disorder, while the persistence of dynamic spin fluctuations down to the lowest temperatures may indicate the survival of QSL-like excitations despite such disorder.