High-resolution magnetostriction measurements of the Pauli-limited superconductor Sr2RuO4

TL;DR

This study used high-resolution magnetostriction measurements on Sr2RuO4 to detect anomalies near the Pauli-limited critical field, providing insights into possible FFLO phase emergence and transition characteristics.

Contribution

It presents the first high-resolution magnetostriction data on Sr2RuO4 under in-plane magnetic fields, revealing anomalies potentially linked to the FFLO phase and first-order transition behavior.

Findings

Detection of a hump-like anomaly in magnetostriction near the critical field

Observation of a double-peak structure in the field-angle derivative

Identification of hysteresis indicating a first-order transition

Abstract

We performed high-resolution magnetostriction measurements on the Pauli-limited superconductor Sr$_2$RuO$_4$ using high-quality single crystals. A first-order superconducting transition, accompanied by pronounced hysteresis, was observed under in-plane magnetic fields, where the relative length change of the sample, $\Delta L/L$, was on the order of $10^{-8}$. To ensure the reliability of the measurements, particular attention was paid to minimizing the influence of magnetic torque, which can significantly affect data under in-plane field configurations, via field-angle-resolved magnetostriction. Within the hysteresis regime, slightly below the Pauli-limited upper critical field, a hump-like anomaly in the magnetostriction coefficient was identified. Furthermore, a characteristic double-peak structure in the field-angle derivative of the magnetostriction provides additional support for this anomaly. Although these findings may reflect a lattice response associated with the emergence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in Sr$_2$RuO$_4$, the possibility of a broadened first-order transition cannot be excluded. Notably, this magnetostriction anomaly qualitatively deviates from the FFLO phase boundary suggested by previous NMR measurements, highlighting the necessity for further experimental and theoretical investigations to elucidate the nature of the FFLO state in this material.