Observation of Pair—Quasiparticle Potential Difference in Non-equilibrium Superconductors

  • John Clarke


A difference V has been observed1 between the pair potential and the “quasi-particle potential” in a superconductor in nonequilibrium, when there is an imbalance between the electronlike and holelike excitations. A current I passed through an Al-Al2O3-Sn tunnel junction at a voltage much higher than the Sn gap Δ(T) injected electronlike excitations into the superconducting Sn where it overlayed the Al and removed condensed pairs from the same region. The pair potential was constant throughout the Sn strip. The quasiparticle potential was measured by a normal metal probe (Cu) overlaying the junction and weakly connected to the Sn via a thin oxide barrier. V was measured between the Sn and Cu strips at points far removed from the nonequilibrium region. The potential difference closely followed the theoretical prediction2,3
$$V = I{\tau _Q}/2{e^2}N(0){g_{NS}}$$
where g NS is the normalized tunneling conductance for a superconductor-normal metal junction and N(0) is the density of states at the Fermi level for electrons of one spin. τ Q is the relaxation time for the imbalance in the population of the electronlike and holelike branches, and for Sn was found to be approximately 4 × 10−10Δ(0)/Δ(T) sec. This result is in quite good agreement with the calculated value2,3 of 2 × 10 −10 Δ(0)/Δ(t) sec.


  1. 1.
    John Clarke, Phys. Rev. Lett. 28, 1363 (1972).CrossRefADSGoogle Scholar
  2. 2.
    M. Tinkham and J. Clarke, Phys. Rev. Lett. 28, 1366 (1972).CrossRefADSGoogle Scholar
  3. 3.
    M. Tinkham. Phys. Rev. B 6, 1747 (1972).CrossRefADSGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1974

Authors and Affiliations

  • John Clarke
    • 1
    • 2
    • 3
  1. 1.Department of PhysicsUniversity of CaliforniaBerkeleyUSA
  2. 2.Inorganic Materials Research DivisionLawrence Berkeley LaboratoryBerkeleyUSA
  3. 3.Royal Society Mond LaboratoryCambridgeEngland

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