1,744 research outputs found
Quasiparticle Interface States in Junctions Involving d-Wave Superconductors
Influence of surface pair breaking, barrier transmission and phase difference
on quasiparticle bound states in junctions with d-wave superconductors is
examined. Based on the quasiclassical theory of superconductivity, an approach
is developed to handle interface bound states. It is shown in SIS' junctions
that low energy bound states get their energies reduced by surface pair
breaking, which can be taken into account by introducing an effective order
parameter for each superconductor at the junction barrier. More interestingly,
for the interface bound states near the continuous spectrum the effect of
surface pair breaking may result in a splitting of the bound states. In the
tunneling limit this can lead to a square root dependence of a nonequilibrium
Josephson current on the barrier transmision, which means an enhancement as
compared to the conventional critical current linear in the transmission.
Reduced broadening of bound states in NIS junctions due to surface pair
breaking is found.Comment: 27 pages, Latex fil
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
Universality versus material dependence of fluctuation forces between metallic wires
We calculate the Casimir interaction between two parallel wires and between a
wire and a metall plate. The dielectric properties of the objects are described
by the plasma, Drude and perfect metal models. We find that at asymptotically
large separation interactions involving plasma wires and/or plates are
independent of the material properties, but depend on the dc conductivity
for Drude wires. Counterintuitively, at intermediate separations the
interaction involving Drude wires can become independent of . At
smaller separations, we compute the interaction numerically and observe an
approach to the proximity approximation
Superconducting Junctions with Ferromagnetic, Antiferromagnetic or Charge-Density-Wave Interlayers
Spectra and spin structures of Andreev interface states and the Josephson
current are investigated theoretically in junctions between clean
superconductors (SC) with ordered interlayers. The Josephson current through
the ferromagnet-insulator-ferromagnet interlayer can exhibit a nonmonotonic
dependence on the misorientation angle. The characteristic behavior takes place
if the pi state is the equilibrium state of the junction in the particular case
of parallel magnetizations. We find a novel channel of quasiparticle reflection
(Q reflection) from the simplest two-sublattice antiferromagnet (AF) on a
bipartite lattice. As a combined effect of Andreev and Q reflections, Andreev
states arise at the AF/SC interface. When the Q reflection dominates the
specular one, Andreev bound states have almost zero energy on AF/ s-wave SC
interfaces, whereas they lie near the edge of the continuous spectrum for
AF/d-wave SC boundaries. For an s-wave SC/AF/s-wave SC junction, the bound
states are found to split and carry the supercurrent. Our analytical results
are based on a novel quasiclassical approach, which applies to interfaces
involving itinerant antiferromagnets. Similar effects can take place on
interfaces of superconductors with charge density wave materials (CDW),
including the possible d-density wave state (DDW) of the cuprates.Comment: LT24 conference proceeding, 2 pages, 1 figur
Transport through superconductor/magnetic dot/superconductor structures
The coupling of two s-wave superconductors through a small magnetic dot is
discussed. Assuming that the dot charging energy is small compared to the
superconducting gap, , and that the moment of the dot is
classical, we develop a simple theory of transport through the dot. The
presence of the magnetic dot will position Andreev bound states within the
superconducting gap at energies tunable with the magnetic properties of the
dot. Studying the Josephson coupling it is shown that the constructed junction
can be tuned from a "0" to a ""-junction via a degenerate two-level state
either by changing the magnetic moment of the dot or by changing temperature.
Furthermore, it is shown that details of the magnetic dot can be extracted from
the sub-harmonic structure in the current-voltage characteristics of the
junction.Comment: 5 pages, 4 figures, paper presented at the conference SDP 2001 in
Tokyo on June 2
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