Spin-liquid signatures in the quantum critical regime of pressurized CePdAl

Abstract

CePdAl is a prototypical frustrated Kondo lattice with partial long-range order (LRO) at TN=2.7 K. Previous bulk experiments under hydrostatic pressure found signatures for a quantum critical regime that extends from pc≈0.9 GPa, where LRO disappears, up to ∼1.7 GPa. We employed extensive muon spin relaxation and rotation experiments under pressure. The continuous and complete suppression of LRO at pc is confirmed. Above TN(p) and beyond pc, an additional crossover scale T∗(p) characterizes the change from pure to stretched exponential relaxation in zero field. Remarkably, T∗(p) agrees with previously determined signatures of entropy accumulation above LRO. This coincidence microscopically evidences fluctuating frustrated spins at T≤T∗ with spin-liquid behavior. Power-law divergences of the temperature and longitudinal field dependences of the relaxation rate, with time-field scaling, at pressures between pc and 1.7 GPa characterize this regime as quantum critical.