Superconducting Energy Gaps from Magnetization Measurements: Pb-In System

Isothermal-magnetization data have been obtained for a series of well-annealed chromeplated Pb-In alloys of In composition between 30 and 80 at.% in the temperature range 1.90 °K to the appropriate transition temperature. The empirical relation proposed by Toxen involving the thermodynamic-critical-field data and the energy gap has been found to be valid over a wide range of values of the Ginzburg-Landau parameter $\kappa$, the electron mean free path $l$, and for both weak and strong coupling alloys. Consequently, it may be used to obtain the energy gap at $T=0\mathrm{}$ from the critical-field measurements both in the case of elemental and alloy superconductors. The experimentally determined Ginzburg-Landau parameters ${\kappa }_1\mathrm{}\left(T\right)\mathrm{}$ and ${\kappa }_2\mathrm{}\left(T\right)\mathrm{}$ show a stronger temperature dependence and are generally larger than predicted by existing weak coupling theories.