Phase Dependent Energy Levels of Bound States and D.C. Josephson Current in Unconventional Superconductor/Ferromagnetic Insulator/Unconventional Superconductor Junctions.

Tanaka Yukio, Kashiwaya Satoshi

doi:10.1143/jpsj.69.1152

Properties of the DC Josephson effects in unconventional-superconductors under the presence of an exchange field in the insulator are studied theoretically. The current-phase relation of the DC Josephson current I( varphi) and the temperature dependence of the maximum Josephson current I_C(T) are calculated for various pairing symmetries and crystal orientations as a function of the exchange interaction strength (I_m). The influences of the spin-orbit coupling are also discussed. The phase dependent energy levels of quasiparticle bound states are sensitive to the magnitude of I_m, orientaions of the junctions, and especially parities of two supercondctors. When the two superconductors have d-wave symmetries, I_C(T) shows non-monotonous behavior on the magnitude of I_m, and accordingly the Josephson junction changes between “0-junction” and “π-junction”. On the other hand, when the two superconductors have different parities, e.g. s-wave and p-wave, the Josephson current is largely suppressed due to SU(2) symmetry in the spin space in the absence of I_m. However, the Josephson current rapidly recovers with the increase of I_m because of the breakdown in SU(2) symmetry. These anomalous features can be used as a criteria for the identification of the pairing symmetries in novel superconductors.

Phase Dependent Energy Levels of Bound States and D.C. Josephson Current in Unconventional Superconductor/Ferromagnetic Insulator/Unconventional Superconductor Junctions.

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