M. Sigrist et al., INFLUENCE OF TWIN BOUNDARIES ON JOSEPHSON-JUNCTIONS BETWEEN HIGH-TEMPERATURE AND CONVENTIONAL SUPERCONDUCTORS, Physical review. B, Condensed matter, 53(5), 1996, pp. 2835-2849
We give a consistent explanation of the c-axis Josephson tunneling exp
eriment by Sun and co-workers between YBa2Cu3O6+x and Pb within the d-
wave pairing scenario. Using a Ginzburg-Landau formulation, orthorhomb
ic deformation and twinning of the crystal lattice are taken into acco
unt. In the presence of orthorhombic distortion, symmetry arguments al
low a c-axis Josephson coupling between YBa2Cu3O6+x and Pb. However, f
or a highly twinned YBa2Cu3O6+x sample, the Josephson coupling is weak
ened due to destructive interference effects. On the other hand, we de
monstrate that destructive effects due to twinning can be:overcome, if
twin boundaries support a state which locally breaks time reversal sy
mmetry and leads to a channel which adds constructively to the total J
osephson coupling. Properties of the Josephson junctions measured in e
xperiment, such as the Fraunhofer pattern and the Fiske resonance, kee
p their standard form for such a junction. The existence of a twin bou
ndary state with broken time reversal symmetry can directly be tested,
for example, by observing vortices with fractional flux quanta on twi
n boundaries.