Yasuhiro Asano

Josephson Effect due to Odd-Frequency Pairs in Diffusive Half Metals

Motivated by a recent experiment [Keizer et al., Nature (London) 439, 825 (2006)], we study the Josephson effect in superconductor/diffusive half metal/superconductor junctions using the recursive Green function method. The spin-flip scattering at the junction interfaces opens the Josephson channel of the odd-frequency spin-triplet Cooper pairs. As a consequence, the local density of states in a half metal has a large peak at the Fermi energy. Therefore the odd-frequency pairs can be detected experimentally by using the scanning tunneling spectroscopy.

Josephson current in s-wave-superconductor/Sr2RuO4 junctions

The Josephson current between an s-wave and a spin-triplet superconductor Sr2RuO4 (SRO) is studied theoretically. In spin-singlet/spin-triplet superconductor junctions, there is no Josephson current proportional to sin phi in the absence of the spin-flip scattering near junction interfaces, where phi is a phase difference across junctions. Thus, a dominant term of the Josephson current is proportional to sin 2phi. The spin-orbit scattering at the interfaces gives rise to the Josephson current proportional to cos phi, which is a direct consequence of the chiral paring symmetry in SRO.

Anomalous features of the proximity effect in triplet superconductors

Anomalous features of the proximity effect specific to diffusive normal metal (DN) / triplet superconductor junctions are studied within the quasiclassical Green?s function formalism. The pair amplitude fN as a function of energy ? in DN, satisfies an anomalous relation, fN(?)=?fN*(??) , contrary to that in singlet superconductor junctions case where fN(?)=fN*(??) . Such an unusual ? dependence is responsible for a zero energy peak in the local density of states and is a source of an anomalous penetration of the applied magnetic field into DN. Our results are relevant to Sr2RuO4 , which is considered to have a px+ipy -wave symmetry.

Phenomenological theory of zero-energy Andreev resonant states

A conceptual consideration is given to a zero-energy state (ZES) at the surface of unconventional superconductors. The reflection coefficients in normal-metal/superconductor (NS) junctions are calculated based on a phenomenological description of the reflection processes of a quasiparticle. The phenomenological theory reveals the importance of the sign change in the pair potential for the formation of the ZES. The ZES is observed as the zero-bias conductance peak (ZBCP) in the differential conductance of NS junctions. The split of the ZBCP due to broken time-reversal symmetry states is naturally understood in the present theory. We also discuss effects of external magnetic fields on the ZBCP.

Disappearance of ensemble-averaged Josephson current in dirty superconductor-normal-superconductor junctions of d-wave superconductors

We discuss the Josephson current in superconductor/dirty normal conductor/superconductor junctions, where the superconductors have

Direct-current Josephson effect in SNS junctions of anisotropic superconductors

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Anomalous josephson effect in p-wave dirty junctions

pairing symmetry. The low-temperature behavior of the Josephson current depends on the orientation angle between the crystalline axis and the normal of the junction interface. We show that the ensemble-averaged Josephson current vanishes when the orientation angle is

Macroscopic quantum tunneling and quasiparticle dissipation in d-wave superconductor Josephson junctions

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Unconventional superconductivity and Josephson effect in superconductor/dirty normal metal/superconductor junctions

and the normal conductor is in the diffusive transport regime. The

Majorana fermions and odd-frequency Cooper pairs in a normal-metal nanowire proximity-coupled to a topological superconductor

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