We study theoretically the Josephson effect in junctions based on unconventional superconductors with diffusive barriers, using the quasiclassical Green's function formalism. Generalized boundary conditions at junction interfaces applicable to unconventional superconductors are derived by calculating a matrix current within the circuit transport theory. Applying these boundary conditions, we have calculated the Josephson current in structures with various pairing symmetries. A number of predictions are made: (a) nonmonotonic temperature dependence in d-wave superconductor/diffusive normal metal/d-wave superconductor (D/DN/D) junctions, (b) anomalous current-phase relations in p-wave superconductor/diffusive normal metal/p-wave superconductor (P/DN/P) junctions, (c) second harmonics in D/DN/D and P/DN/P junctions, (d) a double-peak structure of the critical current in D/DF/D junctions, and (e) enhanced Josephson current by the exchange field in S/DF/P junctions. We have also investigated peculiarities of the Josephson coupling in D/DF/D, P/DF/P, and S/DF/P junctions. An oscillatory behavior of the supercurrent and the second harmonics in the current-phase relation is studied as a function of the length of the diffusive ferromagnet.
|Physical review B: Condensed matter and materials physics
|Published - 2007