18 research outputs found
Geometric pi Josephson junction: Current-phase relations and critical current
Josephson junctions with an intrinsic phase shift of pi, so-called pi
Josephson junctions, can be realized by a weak link of a d-wave superconductor
with an appropriate boundary geometry. A model for the pairing potential of an
according weak link is introduced which allows for the calculation of the
influence of geometric parameters and temperature. From this model,
current-phase relations and the critical current of the device are derived. The
range of validity of the model is determined by comparison with selfconsistent
solutions.Comment: 4 pages, 5 figures. IEEE Trans. Appl. Supercond., accepte
Spectrum of low energy excitations in the vortex state: comparison of Doppler shift method to quasiclassical approach
We present a detailed comparison of numerical solutions of the quasiclassical
Eilenberger equations with several approximation schemes for the density of
states of s- and d-wave superconductors in the vortex state, which have been
used recently. In particular, we critically examine the use of the Doppler
shift method, which has been claimed to give good results for d-wave
superconductors. Studying the single vortex case we show that there are
important contributions coming from core states, which extend far from the
vortex cores into the nodal directions and are not present in the Doppler shift
method, but significantly affect the density of states at low energies. This
leads to sizeable corrections to Volovik's law, which we expect to be sensitive
to impurity scattering. For a vortex lattice we also show comparisons with the
method due to Brandt, Pesch, and Tewordt and an approximate analytical method,
generalizing a method due to Pesch. These are high field approximations
strictly valid close to the upper critical field Bc2. At low energies the
approximate analytical method turns out to give impressively good results over
a broad field range and we recommend the use of this method for studies of the
vortex state at not too low magnetic fields.Comment: 11 pages, 11 figures; revised version, error in Fig. 6b remove
Coherent particle oscillations between two Bose-Einstein condensates mediated by a single localized impurity atom
Effect of Surface Andreev Bound States on the Bean-Livingston Barrier in d-Wave Superconductors
We study the influence of surface Andreev bound states in d-wave
superconductors on the Bean-Livingston surface barrier for entry of a vortex
line into a strongly type-II superconductor. Starting from Eilenberger theory
we derive a generalization of London theory to incorporate the anomalous
surface currents arising from the Andreev bound states. This allows us to find
an analytical expression for the modification of the Bean-Livingston barrier in
terms of a single parameter describing the influence of the Andreev bound
states. We find that the field of first vortex entry is significantly enhanced.
Also, the depinning field for vortices near the surface is renormalized. Both
effects are temperature dependent and depend on the orientation of the surface
relative to the d-wave gap function.Comment: 4 pages, 3 figures; minor changes; accepted for publication in Phys.
Rev. Lett
Local density of states at polygonal boundaries of d-wave superconductors
Besides the well-known existence of Andreev bound states, the zero-energy
local density of states at the boundary of a d-wave superconductor strongly
depends on the boundary geometry itself. In this work, we examine the influence
of both a simple wedge-shaped boundary geometry and a more complicated
polygonal or faceted boundary structure on the local density of states. For a
wedge-shaped boundary geometry, we find oscillations of the zero-energy density
of states in the corner of the wedge, depending on the opening angle of the
wedge. Furthermore, we study the influence of a single Abrikosov vortex
situated near a boundary, which is of either macroscopic or microscopic
roughness.Comment: 10 pages, 11 figures; submitted to Phys. Rev.
Shadow on the wall cast by an Abrikosov vortex
At the surface of a d-wave superconductor, a zero-energy peak in the
quasiparticle spectrum can be observed. This peak appears due to Andreev bound
states and is maximal if the nodal direction of the d-wave pairing potential is
perpendicular to the boundary. We examine the effect of a single Abrikosov
vortex in front of a reflecting boundary on the zero-energy density of states.
We can clearly see a splitting of the low-energy peak and therefore a
suppression of the zero-energy density of states in a shadow-like region
extending from the vortex to the boundary. This effect is stable for different
models of the single Abrikosov vortex, for different mean free paths and also
for different distances between the vortex center and the boundary. This
observation promises to have also a substantial influence on the differential
conductance and the tunneling characteristics for low excitation energies.Comment: 5 pages, 5 figure
Andreev bound states and tunneling characteristics of a non-centrosymmetric superconductor
The tunneling characteristics of planar junctions between a normal metal and
a non-centrosymmetric superconductor like CePt3Si are examined. It is shown
that the superconducting phase with mixed parity can give rise to
characteristic zero-bias anomalies in certain junction directions. The origin
of these zero-bias anomalies are Andreev bound states at the interface. The
tunneling characteristics for different directions allow to test the structure
of the parity-mixed pairing state.Comment: 4 pages, 3 figure
Geometric pi Josephson junction in d-wave superconducting thin films
A novel way to realize a pi Josephson junction is proposed, based on a weak
link in an unconventional d-wave superconductor with appropriately chosen
boundary geometry. The critical current of such a junction is calculated from a
fully selfconsistent solution of microscopic Eilenberger theory of
superconductivity. The results clearly show, that a transition to a pi
Josephson junction occurs for both low temperatures and small sizes of the
geometry.Comment: 3 pages, 3 figure