176 research outputs found
Interplay of spin-discriminated Andreev bound states forming the 0- transition in Superconductor-Ferromagnet-Superconductor Junctions
The Josephson current in S-F-S junctions is described by taking into account
different reflection (transmission) amplitudes for quasiparticles with spin up
and down. We show that the 0- transition in the junctions can take place
at some temperature only for sufficiently strong spin-activity of the
interface. In particular, Andreev interface bound state energies in one spin
channel have to be all negative, while in the other one positive. Only one spin
channel contributes then to the zero-temperature Josephson current. At the
temperature of the 0- transition two spin channels substantially
compensate each other and can result in a pronounced minimum in the critical
current in tunnel junctions. The minimal critical current is quadratic in small
transparency and contains first and second harmonics of one and the same order.Comment: 5 pages, revtex, 2 ps-figure
Influence of the atomic-scale inhomogeneity of the pair interaction on extracted from the STM spectra characteristics of high- superconductors
The influence of the atomic-scale inhomogeneities of the pairing interaction
strength on the superconducting order parameter and the conductance spectra
measurable by STM is studied in the framework of weak-coupling BCS-like theory
for two-dimensional lattice model. First of all, it is found that the
inhomogeneity having the form of atomic-scale regions of enhanced pair
interaction increases the ratio of the local low-temperature gap in
differential conductance spectra to the local temperature of vanishing the gap
. Even in the framework of mean-field treatment this ratio is
shown to be larger than the one corresponding to the homogeneous case. It is
shown that the effect of thermal phase fluctuations of the superconducting
order parameter can further increase this ratio. Taking them into account in
the framework of a toy model we obtained the ratio to be . It is found that the additional atomic-scale hopping element disorder and
weak potential scatterers, which can also take place in cuprate materials, have
no considerable effect on the statistical properties of the system, including
the distribution of the gaps, and the ratio . The second
consequence of the atomic-scale order parameter inhomogeneity is the
anticorrelation between the low-temperature gap and the high-temperature
zero-bias conductance. The obtained results could bear a relation to recent STM
measurements.Comment: 14 pages, 13 figure
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