Bulk evidence for single-gap s-wave superconductivity in the intercalated graphite superconductor C${}_6$Yb

Abstract

We report measurements of the in-plane electrical resistivity $\ddot{I}$ and the thermal conductivity $\hat{I}º$ of the intercalated graphite superconductor C${}_6$Yb to temperatures as low as $T_c$/100. When a field is applied along the c-axis, the residual electronic linear term $\hat{I}{º}_0/T$ evolves in an exponential manner for $H_{c1}<H<H_{c2}$. This activated behaviour establishes the order parameter as unambiguously s-wave, and rules out the possibility of multi-gap or unconventional superconductivity in this system.

4 pages, 4 figs, submitted to Phys. Rev. Lett