Critical pair-breaking current in superconducting aluminum strips far belowTc

Critical currents of narrow, thin aluminum strips have been measured as a function of temperature. For the smallest samples uniformity of the current density is obtained over a large temperature range. Hence the intrinsic limit on the current-carrying capacity of the superconductor was measured outside the Ginzburg-Landau regime. The experimental values are compared with recent theoretical predictions by Kupriyanov and Lukichev. An approximate method of solving their equations is given, the results of which agree with the exact solution to within 1%. Experimental data are in excellent agreement with theoretical predictions. The absolute values agree if one assumes a $\rho l$ value of 4×${10}^{-16\mathrm{}}$ Ω${\mathrm{m}}^2$ with $v_F=1.3\mathrm{}\times {10}^6$ m/s. This value for $\rho l$ is the same as that found from measurements of the anomalous skin effect but differs from values extracted from size-effect-limited resistivity.