Angular Dependent Torque Measurements on CeCoIn${}_5$ Single Crystals

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 $\le T\le$ 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 $\hat{I}¸=90^o$ ($\hat{I}¸$ is the angle between $H$ and the $c-$axis of the crystal), a result of intrinsic pinning of vortices. The anisotropy ${\hat{I}}^3\equiv \sqrt{m_c/m_a}$ 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 ${\hat{I}}^3$ decreases with increasing magnetic field and temperature. The fact that ${\hat{I}}^3$ is not a constant points towards a multiband scenario in this heavy fermion material.