If an electron-like (k>kF) or a hole-like (k<kF) excitation is added to a superconductor, a charge imbalance is created. Charge imbalance is of practical importance first, because it gives rise to a measureable steady-state voltage in a superconductor, and second, because it provides a tool for measuring various electron-relaxation rates. The importance of the disequilibrium of the electron- and hole-like branches was first pointed out by Pippard et al. (1971) who measured the electrical resistance of superconductor-normal metal-superconductor (SNS) sandwiches as a function of temperature. Near the superconducting transition temperature, Tc, they found that the resistance increased with increasing temperature. They ascribed this increase to the propagation of quasiparticles having a branch imbalance distribution into or out of the superconductor, a process that, at the time, they believed generated a potential step at each NS interface, and thus produced an additional boundary resistance. However, the first quantitative understanding of charge imbalance arose from experiments in which electrons were injected via a tunnel junction into a superconducting film (Clarke 1972); at the time this experiment was performed, its connection with the NS interface resistance was not apparent.


Boltzmann Equation Elastic Scattering Tunnel Junction Charge Imbalance Charge Relaxation 
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Copyright information

© Plenum Press, New York 1981

Authors and Affiliations

  • John Clarke
    • 1
    • 2
  1. 1.Department of PhysicsUniversity of CaliforniaBerkeleyUSA
  2. 2.Materials and Molecular Research DivisionLawrence Berkeley LaboratoryBerkeleyUSA

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