Electric Potential Near a Superconducting Boundary

Abstract

In the nonequilibrium region close to a current-carrying superconducting—normal (S/N) interface Rieger et al.¹ proposed a concept of separate chemical potentials for quasiparticles and pairs. From a time-dependent Ginzburg—Landau (GL) approach they found that the difference in pair potential µ _p and electron potential µ _e depends on the divergence of the supercurrent j _s in the following way:

$${{\mu }_{p}}\,-\,{{\mu }_{e\,}}\,=\,(m{{\zeta }^{2}}/4e\tau {{\left| \psi \right|}^{2}})\,\nabla \,\centerdot \,{{j}_{s}}$$

(1)

where τ is the GL relaxation time, ξ is the coherence distance, and ψ is the amplitude of the condensed phase. It was also found that µ _P remains constant even near a S/N boundary where ∇·j _s is nonzero. In a recent paper² we reported experimental evidence for this concept and found that a superconducting voltage probe measures the pair chemical potential and a normal voltage probe measures the quasiparticle chemical potential. These measurements were made with tantalum thin-film microcircuits fabricated with photoetch and selective anodization techniques. The transition temperature of these films is thickness dependent² and the relative transition temperature of different regions was determined by the respective thicknesses, which in turn were controlled by the anodization process.

Work supported in part by the Office of Naval Research, Contract No. N00014-67-A-0094-0013.

Supported by a Schlumberger Foundation Fellowship.