title: Degenerate ground state in a mesoscopic YBa2Cu3O(7-x) grain boundary Josephson junction.
abstract: We have measured the current-phase relationship I(varphi) of symmetric 45 degrees YBa2Cu3O7-x grain boundary Josephson junctions. Substantial deviations of the Josephson current from conventional tunnel-junction behavior have been observed: (i) The critical current exhibits, as a function of temperature T, a local minimum at a temperature T*. (ii) At T approximately T*, the first harmonic of I(phi) changes sign. (iii) For T<T*, the second harmonic of I(phi) is comparable to the first harmonic, and (iv) the ground state of the junction becomes degenerate. The results are in good agreement with a microscopic model of Josephson junctions between d-wave superconductors.
authors.affiliation: Department of Cryoelectronics, Institute for Physical High Technology, P.O. Box 100239, D-07702 Jena, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Il'ichev
authors.forename: M
authors.initials: M
authors.lastname: Grajcar
authors.forename: R
authors.initials: R
authors.lastname: Hlubina
authors.forename: R P
authors.initials: RP
authors.lastname: IJsselsteijn
authors.forename: H E
authors.initials: HE
authors.lastname: Hoenig
authors.forename: H G
authors.initials: HG
authors.lastname: Meyer
authors.forename: A
authors.initials: A
authors.lastname: Golubov
authors.forename: M H
authors.initials: MH
authors.lastname: Amin
authors.forename: A M
authors.initials: AM
authors.lastname: Zagoskin
authors.forename: A N
authors.initials: AN
authors.lastname: Omelyanchouk
authors.forename: M Y
authors.initials: MY
authors.lastname: Kupriyanov