Angular Dependent Torque Measurements on CeCoIn$_5$ Single Crystals

TL;DR

This study investigates the angular dependence of torque in CeCoIn$_5$ single crystals, revealing a decreasing anisotropy with field and temperature, suggesting multiband superconductivity in this heavy fermion material.

Contribution

It provides the first detailed angular torque measurements on CeCoIn$_5$, demonstrating anisotropy variation and evidence for multiband effects in its superconducting state.

Findings

Anisotropy decreases with increasing magnetic field and temperature.

Sharp hysteresis peaks indicate intrinsic vortex pinning.

Evidence suggests multiband superconductivity in CeCoIn$_5$.

Abstract

Angular dependent torque measurements were performed on single crystals of CeCoIn$_5$, a heavy fermion superconductor ($T_{c0}$ = 2.3 K), in the temperature, $T$, range 1.9 K $\leq T \leq $ 20 K and magnetic fields $H$ up to 14 T. A large paramagnetic effect is found in the normal state. Torque measurements in the mixed state were also performed. The torque curves show sharp hysteresis peaks at $\theta = 90^{o}$ ($\theta$ is the angle between $H$ and the $c-$axis of the crystal), a result of intrinsic pinning of vortices. The anisotropy $\gamma \equiv \sqrt{m_{c}/m_{a}}$ in the mixed state was determined from the reversible part of the vortex contribution to the torque signal using Kogan's model [Phys. Rev. B \textbf{38}, 7049 (1988)]. The anisotropy $\gamma$ decreases with increasing magnetic field and temperature. The fact that $\gamma$ is not a constant points towards a multiband scenario in this heavy fermion material.