Superconductivity in the Correlated Pyrochlore Cd_2Re_2O_7

Abstract

We report the observation of superconductivity in high-quality Cd$_2$Re$_2$O$_7$ single crystals with room-temperature pyrochlore structure. Resistivity and ac susceptibility measurements establish an onset transition temperature T$_c^{onset}$ = 1.47 K with transition width $Δ$T$_c$ = 0.25 K. In applied magnetic field, the resistive transition shows a type-II character, with an approximately linear temperature-dependence of the upper critical field H$_{c2}$. The bulk nature of the superconductivity is confirmed by the specific heat jump with $Δ$C = 37.9 mJ/mol-K. Using the $γ$ value extracted from normal-state specific heat data, we obtain $Δ$C/$γ$T$_c$ = 1.29, close to the weak coupling BCS value. In the normal state, a negative Hall coefficient below 100 K suggests electron-like conduction in this material. The resistivity exhibits a quadratic T-dependence between 2 and 60 K, i.e., $ρ=ρ_0$+AT$^2$, indicative of Fermi-liquid behavior. The values of the Kadowaki-Woods ratio A/$γ^2$ and the Wilson ratio are comparable to that for strongly correlated materials.