10 research outputs found
Josephson current in graphene: the role of unconventional pairing symmetries
We investigate the Josephson current in a graphene
superconductor/normal/superconductor junction, where superconductivity is
induced by means of the proximity effect from external contacts. We take into
account the possibility of anisotropic pairing by also including singlet
nearest-neighbor interactions, and investigate how the transport properties are
affected by the symmetry of the superconducting order parameter. This
corresponds to an extension of the usual on-site interaction assumption, which
yields an isotropic s-wave order parameter near the Dirac points. Here, we
employ a full numerical solution as well as an analytical treatment, and show
how the proximity effect may induce exotic types of superconducting states near
the Dirac points, e.g. - and -wave pairing or a combination of s-wave
and p+\i p-wave pairing. We find that the Josephson current exhibits a
weakly-damped, oscillatory dependence on the length of the junction when the
graphene sheet is strongly doped. The analytical and numerical treatments are
found to agree well with each other in the s-wave case when calculating the
critical current and current-phase relationship. For the scenarios with
anisotropic superconducting pairing, there is a deviation between the two
treatments, especially for the effective -wave order parameter near the
Dirac cones which features zero-energy states at the interfaces. This indicates
that a numerical, self-consistent approach becomes necessary when treating
anisotropic superconducting pairing in graphene.Comment: 15 pages, 12 figure
Diagrammatic Quantum Monte Carlo solution of the two-dimensional Cooperon-Fermion model
We investigate the two-dimensional cooperon-fermion model in the correlated
regime with a new continuous-time diagrammatic determinant quantum Monte Carlo
(DDQMC) algorithm. We estimate the transition temperature , examine the
effectively reduced band gap and cooperon mass, and find that delocalization of
the cooperons enhances the diamagnetism. When applied to diamagnetism of the
pseudogap phase in high- cuprates, we obtain results in a qualitative
agreement with recent torque magnetization measurements.Comment: 8 pages, 11 figure
Considerable enhancement of the critical current in a superconducting film by magnetized magnetic strip
We show that a magnetic strip on top of a superconducting strip magnetized in
a specified direction may considerably enhance the critical current in the
sample. At fixed magnetization of the magnet we observed diode effect - the
value of the critical current depends on the direction of the transport
current. We explain these effects by a influence of the nonuniform magnetic
field induced by the magnet on the current distribution in the superconducting
strip. The experiment on a hybrid Nb/Co structure confirmed the predicted
variation of the critical current with a changing value of magnetization and
direction of the transport current.Comment: 6 pages, 7 figure