Signatures of a Quantum Griffiths Phase close to an Electronic Nematic Quantum Phase Transition

TL;DR

This study provides evidence of a quantum Griffiths phase near a nematic quantum critical point in FeSe$_{0.89}$S$_{0.11}$, characterized by power-law scaling and a diverging dynamical exponent, influenced by disorder and Fermi surface topology.

Contribution

First experimental observation of a quantum Griffiths phase associated with a nematic quantum critical point in an iron-based superconductor.

Findings

Magnetoresistivity isotherms show a crossing indicative of a Griffiths phase.

Dynamical exponent varies continuously over a broad temperature range.

Fermi liquid behavior emerges at low temperatures due to nematoelastic coupling and a Lifshitz transition.

Abstract

In the vicinity of a quantum critical point, quenched disorder can lead to a quantum Griffiths phase, accompanied by an exotic power-law scaling with a continuously varying dynamical exponent that diverges in the zero-temperature limit. Here, we investigate a nematic quantum critical point in the iron-based superconductor FeSe$_{0.89}$S$_{0.11}$ using applied hydrostatic pressure. We report an unusual crossing of the magnetoresistivity isotherms in the non-superconducting normal state which features a continuously varying dynamical exponent over a large temperature range. We interpret our results in terms of a quantum Griffiths phase caused by nematic islands that result from the local distribution of Se and S atoms. At low temperatures, the Griffiths phase is masked by the emergence of a Fermi liquid phase due to a strong nematoelastic coupling and a Lifshitz transition that changes the topology of the Fermi surface.