Low-Temperature Thermal Conductivity of CeRh₂As₂

CeRh$_2$As$_2$ is a rare unconventional superconductor ($T_c=0.26$ K) characterized by two adjacent superconducting phases for a magnetic field $H \parallel c$-axis of the tetragonal crystal structure. Antiferromagnetic order, quadrupole-density-wave order ($T_0 = 0.4$ K) and the proximity of this material to a quantum-critical point have also been reported: The coexistence of these phenomena with superconductivity is currently under discussion. Here, we present thermal conductivity and electrical resistivity measurements on a single crystal of CeRh$_2$As$_2$ between 60 mK and 200 K and in magnetic fields ($H \parallel c$) up to 8 T. Our measurements at low $T$ verify the Wiedemann-Franz law within the error bars. The $T$ dependence of the thermal conductivity $\kappa(T)$ shows a pronounced drop below $T_c$ which is also field dependent and thus interpreted as the signature of superconductivity. However, the large residual resistivity and the lack of sharp anomalies in $\kappa(T)$ at the expected transition temperatures clearly indicate that samples of much higher purity are required to gain more information about the superconducting gap structure.