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

CePdAl is a prototypical frustrated Kondo lattice with partial long-range order (LRO) at T N = 2 . 7 K. Previous bulk experiments under hydrostatic pressure found signatures for a quantum critical regime that extends from p c ≈ 0 . 9 GPa, where LRO disappears, up to ∼ 1 . 7 GPa. We employed extensive muon spin relaxation and rotation ( µ SR) experiments under pressure. The continuous and complete suppression of LRO at p c is confirmed. Above T N ( p ) and beyond p c , 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 p c and 1.7 GPa characterize this regime as quantum critical.