Zero-energy bound states in superconductor/ferromagnet superlattices

• Published in: Physica. C, Superconductivity Vol. 320; no. 3; pp. 259 - 266
• Main Authors: Prokic, V, Dobrosavljevic-Grujic, L
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.07.1999
• Subjects: Josephson supercurrent; Superconductor/ferromagnet superlattices; Zero-energy bound states; 74.80.Dm; Superconductor/ferromagnet superlattices; Josephson supercurrent; Zero-energy bound states; 74.50.+r
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/S0921-4534(99)00345-7

Andreev bound states in monoatomic superconductor–ferromagnet (S/F) superlattices are studied theoretically, assuming tunneling between S and F layers in perpendicular direction. Andreev reflection at S/F interfaces is strongly affected by the exchange interaction h in F layers. In the ground state, only for h≠0 zero-energy states (ZES) are formed on S and F layers. For h=0, corresponding to superconductor–normal metal (S/N) superlattices, ZES may appear in the nonequilibrium phase, ϕ= π. This is found both for s-wave and d-wave symmetry of the order parameter in S. The conditions for ZES are obtained as a function of h, of the transfer integral t for movement of quasiparticles (QPs) between S and F layers, and of the corresponding ground state phase difference ϕ e q between two neighboring S layers.