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 ${T}_{\mathrm{N}}=2.7$ K. Previous bulk experiments under hydrostatic pressure found signatures for a quantum critical regime that extends from ${p}_{\mathrm{c}}\ensuremath{\approx}0.9$ GPa, where LRO disappears, up to $\ensuremath{\sim}1.7$ GPa. We employed extensive muon spin relaxation and rotation experiments under pressure. The continuous and complete suppression of LRO at ${p}_{\mathrm{c}}$ is confirmed. Above ${T}_{\mathrm{N}}(p)$ and beyond ${p}_{\mathrm{c}}$, 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 $T\ensuremath{\le}{T}^{*}$ 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.