Theory of Surface Energies in Pure Superconductors

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Abstract
The WKBJ variational scheme developed by Bardeen et al. which simplifies the Bogoliubov theory for inhomogeneous superconducting states, has been applied to study normal-superconducting phase boundaries in pure metals. The surface energy of a planar phase boundary at absolute-zero temperature is found for various values of the Ginzburg-Landau parameter. The order parameter and the magnetic field are also determined in this variational procedure. The present theory differs from the existing ones in its being microscopic and nonlocal, but the nonlocality of our theory is found to have small, though not negligible, effects. Near the transition temperature the free-energy expression for planar phase boundaries is examined by an asymptotic expansion method.