287 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
Broadening of Andreev-Bound States in d_{x^2-y^2} superconductors
We investigate the broadening of the bound states at an interface of an
unconventional superconductor by bulk impurity scattering. We use the
quasiclassical theory and include impurity scattering in the Born and in the
unitarity limit. The broadening of bound states due to unitary scatterers is
shown to be substantially weaker than in the Born limit. We study various model
geometries and calculate the temperature dependence of the Josephson critical
current in the presence of these impurity-broadened bound states.Comment: 6 page including 7 figures, submitted to Phys. Rev.
Combined Paramagnetic and Diamagnetic Response of YBCO
It has been predicted that the zero frequency density of states of YBCO in
the superconducting phase can display interesting anisotropy effects when a
magnetic field is applied parallel to the copper-oxide planes, due to the
diamagnetic response of the quasi-particles. In this paper we incorporate
paramagnetism into the theory and show that it lessens the anisotropy and can
even eliminate it altogether. At the same time paramagnetism also changes the
scaling with the square root of the magnetic field first deduced by Volovik
leading to an experimentally testable prediction. We also map out the analytic
structure of the zero frequency density of states as a function of the
diamagnetic and paramagnetic energies. At certain critical magnetic field
values we predict kinks as we vary the magnetic field. However these probably
lie beyond currently accessible field strengths
Repulsive Casimir Force: Sufficient Conditions
In this paper the Casimir energy of two parallel plates made by materials of
different penetration depth and no medium in between is derived. We study the
Casimir force density and derive analytical constraints on the two penetration
depths which are sufficient conditions to ensure repulsion. Compared to other
methods our approach needs no specific model for dielectric or magnetic
material properties and constitutes a complementary analysis.Comment: 11 pages. 3 figures. Misprints corrected in Eq. (4
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