Figure 2

Sample specification. Panels (a–d) refer to the zero magnetic field. (a) The dc resistivity as a function of temperature provides the critical temperature \(T_c=87.6\) K. Extrapolation of the normal-state resistivity below \(T_c\) gives negligible residual resistivity. (b) The imaginary part of conductivity as a function of frequency for several temperatures. The two-fluid model (lines) reproduces the data (symbols) for the superconducting fraction \(f_s=1-T^4/T_c^4\) (line), which is compared in (c) with the fitted values. (d) The real (circles) and imaginary (squares) components of the complex conductivity at 100 K provide the relaxation time \(\tau _N=47\) fs. (e) The measured real part of conductivity for linearly polarized light at magnetic field 7 T (circles) compared with fits based on the vortex dynamics, \(\sigma =\tfrac{1}{2}(\sigma _++\sigma _-)\), supports small pinning with \(\kappa =2\times 10^5\) N/m\(^2\).