FFLO State and Peak Effect Dynamics in CeCoIn_5: Magnetization Studies

TL;DR

This study investigates the FFLO superconducting state in CeCoIn_5 through magnetization measurements, revealing its persistence across different orientations and identifying a peak effect linked to metastable phases near the FFLO transition.

Contribution

It provides new evidence for the FFLO state in CeCoIn_5 across multiple field orientations and uncovers anomalous peak effects indicating complex phase dynamics.

Findings

FFLO state observed for both in-plane and out-of-plane magnetic fields.

Anomalous peak effect detected below the crossover field at low temperatures.

Metastable phases suggested near the FFLO transition.

Abstract

Magnetization measurements were performed on CeCoIn_5 at temperature down to 30 mK with the magnetic field applied in three different orientations: parallel, near parallel ($\sim$ 10$^{0}$ rotated) and perpendicular to the ab-plane. For these three orientations we have observed crossover features in the torque/magnetization traces at fields just below $H_{c2}$, giving further evidence for the formation of a high field Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) superconducting state in CeCoIn_5 for $H \parallel ab$-plane and newly indicates that the FFLO state persists for out-of-plane field orientations. Furthermore, for the (near) parallel to $ab$-plane field configurations and $T\leq \mathrm{50 mK}$, we have found an anomalous peak effect(APE) just below the crossover field when the magnetic field is sweeping down from normal to superconducting state. The dynamics of this peak suggests the existence of a metastable phase occurring in the vicinity of the FFLO phase and raises questions about the order (first or second) of the transition from FFLO to the superconducting state. None of the above features were found in a Ce_{0.98}Gd_{0.02}CoIn_{5} crystal.