226 research outputs found
Transition Radiation of Moving Abrikosov Vortices
We show that Abrikosov vortices moving towards the surface of a
superconductor emit electromagnetic radiation into free space. The frequency
distribution of the radiated intensity displays a pronounced maximum at
microwave frequencies around v_x/lambda, where lambda is the magnetic
penetration length. Coherent motion of a lattice of flux lines leads to
constructive interference and increases the strength of the radiated power by a
large factor.Comment: 4 pages, 1 figure The new version includes a derivation of novel
dynamical London equations for a moving Abrikosov vortex, as well as a
detailed discussion of boundary condition
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
Strong surface contribution to the Nonlinear Meissner Effect
We demonstrate that in a d-wave superconductor the bulk nonlinear Meissner
effect is dominated by a surface effect due to Andreev bound states at low
temperatures. The contribution of this surface effect to the nonlinear response
coefficient follows a 1/T^3 law with opposite sign compared to the bulk 1/T
behavior. The cross-over from bulk dominated behavior to surface dominated
behavior occurs at a temperature of T/T_c ~ 1/sqrt(kappa). We present an
approximate analytical calculation, which supports our numerical calculations
and provides a qualitative understanding of the effect. The effect can be
probed by intermodulation distortion experiments.Comment: 4 pages, 3 figure
Dynamic electromagnetic response of three-dimensional Josephson junction arrays
We present a theoretical study on the dynamical properties of
three-dimensional arrays of Josephson junctions. Our results indicate that such
superconducting networks represent highly sensitive 3D-SQUIDs having some major
advantages in comparison with conventional planar SQUIDs. The voltage response
function of 3D-SQUIDs is directly related to the vector-character of external
electromagnetic fields. The theory developed here allows the three-dimensional
reconstruction of a detected external field including phase information about
the field variables. Applications include the design of novel magnetometers,
gradiometers and particle detectors.Comment: 5 pages, 9 figures, submitted to Journal of Applied Physic
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
Phase diagram of geometric d-wave superconductor Josephson junctions
We show that a constriction-type Josephson junction realized by an epitactic
thin film of a d-wave superconductor with an appropriate boundary geometry
exhibits intrinsic phase differences between 0 and pi depending on geometric
parameters and temperature. Based on microscopic Eilenberger theory, we provide
a general derivation of the relation between the change of the free energy of
the junction and the current-phase relation. From the change of the free
energy, we calculate phase diagrams and discuss transitions driven by geometric
parameters and temperature.Comment: 9 pages, 11 figures. Phys. Rev. B, accepte
Vortex state in double transition superconductors
Novel vortex phase and nature of double transition field are investigated by
two-component Ginzburg-Landau theory in a situation where fourfold-twofold
symmetric superconducting double transition occurs. The deformation from 60
degree triangular vortex lattice and a possibility of the vortex sheet
structure are discussed. In the presence of the gradient coupling, the
transition changes to a crossover at finite fields. These characters are
important to identify the multiple superconducting phase in PrOs_4_Sb_12.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
High performance magnetic field sensor based on Superconducting Quantum Interference Filters
We have developed an absolute magnetic field sensor using Superconducting
Quantum Interference Filter (SQIF) made of high-T_c grain boundary Josephson
junctions. The device shows the typical magnetic field dependent voltage
response V(B), which is sharp delta-like dip in the vicinity of zero magnetic
field. When the SQIF is cooled with magnetic shield, and then the shield is
removed, the presence of the ambient magnetic field induces a shift of the dip
position from B_0 ~ 0 to a value B ~ B_1, which is about the average value of
the earth magnetic field, at our latitude. When the SQIF is cooled in the
ambient field without shielding, the dip is first found at B ~ B_1, and the
further shielding of the SQIF results in a shift of the dip towards B_0 ~ 0.
The low hysteresis observed in the sequence of experiments (less than 5% of
B_1) makes SQIFs suitable for high precision measurements of the absolute
magnetic field. The experimental results are discussed in view of potential
applications of high-T_c SQIFs in magnetometry.Comment: 4 pages, 2 figure
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