Tunneling, Density of States, and Josephson Effect
The tunneling current through a superconducting-normal (SN) junction or a superconducting-superconducting (SS) junction provides rich information about the quasiparticle density of states and condensate wave function. On the basis of the linear response theory developed in the previous chapter, we first derive a general expression for the tunneling current applicable to both junctions as (12.31). It is subsequently applied to SN junctions to show that the current-voltage characteristics directly reflect the quasiparticle density of states as Fig. 12.2. Next, we consider SS junctions to clarify that, besides extra structures caused by two kinds of the quasiparticle density of states, there appears a new feature at zero bias due to the Josephson effect, as seen in Fig. 12.4, that depends on the phase difference of the two coupled superconductors. Thus, a weak contact between two superconductors provides a unique means to detect the phase of the condensate wave function.
KeywordsTunneling Current Josephson Effect Josephson Current Chemical Potential Difference London Penetration Depth
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