Determination of gap symmetry from angle-dependent Hc2 measurements on CeCu2Si2

Abstract

The tetragonal heavy-fermion compound ccs exhibits a superconducting ground state (S type, $T_c=0.67$ K) close to a magnetic instability. Here, we present angle-resolved resistivity measurements of the upper critical field hc. In-plane rotation of S-type ccs single crystals reveals a four-fold oscillation of $H_{c2}$. An extended weak-coupling BCS model for a d-wave symmetry including strong Pauli-limiting effects confirms the aforementioned angular dependence and points towards d$_{xy}$ symmetry of the order parameter.