Degenerate ground state in a mesoscopic YBa2Cu3O(7-x) grain boundary Josephson junction.
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.
Il'ichev
E
E
Department of Cryoelectronics, Institute for Physical High Technology, P.O. Box 100239, D-07702 Jena, Germany.
Grajcar
M
M
Hlubina
R
R
IJsselsteijn
R P
RP
Hoenig
H E
HE
Meyer
H G
HG
Golubov
A
A
Amin
M H
MH
Zagoskin
A M
AM
Omelyanchouk
A N
AN
Kupriyanov
M Y
MY