%N 6
%V 98
%A M Sutherland
%A N Doiron-Leyraud
%A L Taillefer
%A T Weller
%A M Ellerby
%A SS Saxena
%T Bulk evidence for single-gap s-wave superconductivity in the intercalated graphite superconductor C6Yb
%D 2007
%L discovery116271
%J PHYS REV LETT
%K THERMAL-CONDUCTIVITY, FIELD, STATE, MODEL
%I AMERICAN PHYSICAL SOC
%O © 2007 The American Physical Society
%X We report measurements of the in-plane electrical resistivity rho and thermal conductivity kappa of the intercalated graphite superconductor C6Yb down to temperatures as low as T-c/100. When a field is applied along the c axis, the residual electronic linear term kappa(0)/T evolves in an exponential manner for H-c1 < H < H-c2/2. This activated behavior is compelling evidence for an s-wave order parameter, and is a strong argument against the possible existence of multigap superconductivity.