Influence of twin boundaries on Josephson junctions between high-temperature and conventional superconductors

Abstract

We give a consistent explanation of the c-axis Josephson tunneling experiment by Sun and co-workers between YBa 2 Cu 3 O 6ϩx and Pb within the d-wave pairing scenario. Using a Ginzburg-Landau formulation, orthorhombic deformation and twinning of the crystal lattice are taken into account. In the presence of orthorhombic distortion, symmetry arguments allow a c-axis Josephson coupling between YBa 2 Cu 3 O 6ϩx and Pb. However, for a highly twinned YBa 2 Cu 3 O 6ϩx sample, the Josephson coupling is weakened due to destructive interference effects. On the other hand, we demonstrate that destructive effects due to twinning can be overcome, if twin boundaries support a state which locally breaks time reversal symmetry and leads to a channel which adds constructively to the total Josephson coupling. Properties of the Josephson junctions measured in experiment, such as the Fraunhofer pattern and the Fiske resonance, keep their standard form for such a junction. The existence of a twin boundary state with broken time reversal symmetry can directly be tested, for example, by observing vortices with fractional flux quanta on twin boundaries.

Josephson interferometer in a ring topology as a proof of the symmetry ofSr2RuO4

“…There is a staggered phase for the d x 2 −y 2 -component. This would give rise to compensating contributions of the two domains to the Josephson effect, similar to the situation discussed in the context of c-axis junction between an s-wave and a twinned hightemperature superconductor 38,39 . In addition, this configuration could give rise to spontaneous half-quanta flux lines wherever a domain wall hits the junction perpendicularly.…”

Observation of the second harmonic in superconducting current-phase relation of Nb/Au/(001)YBa 2 Cu 3 O x heterojunctions

“…(i) Sigrist et al have suggested that the phase of the s-wave component in YBCO does not simply jump from 0 to π upon crossing the twin boundary, but rather changes in a smooth way, attaining the value of π/2 right at the twin boundary [7]. The twinned YBCO sample is thus assumed to exhibit a macroscopic d + is pairing symmetry.…”

Asymmetric Magnetic Interference Patterns in 0-πJosephson Junctions

“…However, YBCO has orthorhombic symmetry which implies that the order parameter cannot be purely d-wave and must contain an additional s-wave contribution [9][10][11][12][13]. This has significant consequences for c-axis Josephson tunneling experiments between YBCO and Pb (a standard s-wave superconductor).…”

“…The relative phase α is fixed by the bulk free energy of YBCO and is 0 for one type of twin domain and π for the other [10,11]. The intrinsic phase shift of the junction is determined by α.…”