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

TL;DR

This study uses muon spin relaxation experiments to identify spin-liquid behavior and quantum criticality in pressurized CePdAl, revealing a regime of fluctuating frustrated spins above the long-range order suppression point.

Contribution

The paper provides microscopic evidence of spin-liquid signatures and quantum critical behavior in CePdAl under pressure, extending understanding of frustrated Kondo lattices.

Findings

Suppression of long-range order at critical pressure p_c confirmed.

Identification of a crossover temperature T* associated with entropy accumulation.

Observation of power-law divergences indicating quantum criticality.

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 $p_\mathrm{c} \approx 0.9$ GPa, where LRO disappears, up to $\sim 1.7$ GPa. We employed extensive muon spin relaxation and rotation ($\mu$SR) 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 $T^\ast(p)$ characterizes the change from pure to stretched exponential relaxation in zero field. Remarkably $T^\ast(p)$ agrees with previously determined signatures of entropy accumulation above LRO. This coincidence microscopically evidences fluctuating frustrated spins at $T\leq T^\ast$ 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.