Microscopic evidence of a field-induced critical spin-liquid state in a frustrated metal

TL;DR

This study provides microscopic evidence of a field-induced critical spin-liquid state in a metallic frustrated compound, CePdAl, revealing a transition from magnetic order to a quantum spin liquid with non-Fermi liquid behavior under magnetic fields.

Contribution

It is the first microscopic investigation demonstrating a field-induced critical spin-liquid state in a metallic frustrated system using TF-$bmu$SR techniques.

Findings

Long-range magnetic order at B b1 B_{c2}

Divergence of relaxation rate indicating critical spin-liquid behavior

Observation of non-Fermi liquid state beyond B_{c2}

Abstract

A field-induced quantum spin liquid (QSL) state is an extraordinary phenomenon, hitherto unobserved in metallic frustrated compounds. Recent bulk measurements have revealed intriguing field-induced magnetic states in metallic frustrated CePdAl. However, the nature of these field-induced states, potentially including a QSL state, remains unclear due to the lack of detailed microscopic investigation. To elucidate these field-induced states, we employed the transverse-field muon spin relaxation/rotation (TF-$\mu$SR) technique, applying various magnetic fields parallel to the c-axis in single-crystalline CePdAl over a broad temperature range (100~K-100~mK). Our $\mu$SR data indicate that field-induced low-temperature states for fields B$\leq B_{c2}(=3.4~T)$ exhibit long-range magnetic order, whereas for B>$B_{c2}$ they yield contrasting behavior. Notably, at 3.75 T, the transverse relaxation rate ($\lambda_T$) diverges following a power-law dependence below 800~mK along with an indication of finite frustration, whereas the Knight shift is temperature independent. These observations corroborate the signature of a critical spin-liquid (CSL) with antiferromagnetic spin fluctuations. Furthermore, at 4.3 T, a non-Fermi liquid state is observed where frustration is absent. This comprehensive microscopic study strongly suggests the existence of a CSL state in a metallic frustrated system.