1,839 research outputs found
3D-xy critical properties of YBa2Cu4O8 and magnetic field induced 3D to 1D crossover
We present reversible magnetization data of a YBa2Cu4O8 single crystal and
analyze the evidence for 3D-xy critical behavior and a magnetic field induced
3D to 1D crossover. Remarkable consistency with these phenomena is observed in
agreement with a magnetic field induced finite size effect, whereupon the
correlation length transverse to the applied magnetic field cannot grow beyond
the limiting magnetic length scale L_H. By applying the appropriate scaling
form we obtain the zero-field critical temperature, the 3D to 1D crossover, the
vortex melting line and the universal ratios of the related scaling variables.
Accordingly there is no continuous phase transition in the (H,T)-plane along
the H_c2-lines as predicted by the mean-field treatment.Comment: 8 pages, 4 figure
Experimental phase diagram of moving vortices
In the mixed state of type II superconductors, vortices penetrate the sample
and form a correlated system due to the screening of supercurrents around them.
Interestingly, we can study this correlated system as a function of density and
driving force. The density, for instance, is controlled by the magnetic field,
B, whereas a current density j acts as a driving force F=jxB on all vortices.
The free motion of vortices is inhibited by the presence of an underlying
potential, which tends to pin the vortices. Hence, to minimize the pinning
strength we studied a superconducting glass in which the depinning current is
10 to 1000 times smaller than in previous studies, which enables us to map out
the complete phase diagram in this new regime. The diagram is obtained as a
function of B, driving current and temperature and led a remarkable set of new
results, which includes a huge peak effect, an additional reentrant depinning
phase and a driving force induced pinning phase.Comment: 4 page
Superconductor-Ferromagnet Bi-Layers: a Comparison of s-Wave and d-Wave Order Parameters
We study superconductor-ferromagnet bi-layers, not only for s-wave but also
for d-wave superconductors. We observe oscillations of the critical temperature
when varying the thickness of the ferromagnetic layer for both s-wave and
d-wave superconductors. However, for a rotated d-wave order parameter the
critical temperature differs considerably from that for the unrotated case. In
addition we calculate the density of states for different thicknesses of the
ferromagnetic layer; the results reflect the oscillatory behaviour of the
superconducting correlations.Comment: 11 pages, 5 figures, accepted for publication in J. Phys.: Condens.
Matte
Tilt Modulus and Angle-Dependent Flux Lattice Melting in the Lowest Landau Level Approximation
For a clean high-T superconductor, we analyze the Lawrence-Doniach free
energy in a tilted magnetic field within the lowest Landau level (LLL)
approximation. The free energy maps onto that of a strictly -axis field, but
with a reduced interlayer coupling. We use this result to calculate the tilt
modulus of a vortex lattice and vortex liquid. The vortex contribution
to can be expressed in terms of the squared -axis Josephson plasmon
frequency . The transverse component of the field has very
little effect on the position of the melting curve.Comment: 8 pages, 2 figures, accepted for publication in Physical Review B
(Rapid Communications
Diffusive conductors as Andreev interferometers
We present a novel mechanism of phase-dependent electric transport in
diffusive normal metal-superconductor structures. We provide a detailed
theoretical and numerical analysis of recent unexplained experiments
essentially explaining them.Comment: Self extracting file, 7 pages latex and 4 postscript figures. The
paper is also available at http://www.tn.tudelft.nl/tn/thspap.html In this
revision we resolved some printing problems concerning figures 2 and
Muon Spin Relaxation and Susceptibility Studies of Pure and Doped Spin 1/2 Kagom\'{e}-like system (CuZn)VO(OH) 2HO
Muon spin relaxation (SR) and magnetic susceptibility measurements have
been performed on the pure and diluted spin 1/2 kagom\'{e} system
(CuZn)VO(OH) 2HO. In the pure
system we found a slowing down of Cu spin fluctuations with decreasing
temperature towards K, followed by slow and nearly
temperature-independent spin fluctuations persisting down to = 50 mK,
indicative of quantum fluctuations. No indication of static spin freezing was
detected in either of the pure (=1.0) or diluted samples. The observed
magnitude of fluctuating fields indicates that the slow spin fluctuations
represent an intrinsic property of kagom\'e network rather than impurity spins.Comment: 4 pges, 4 color figures, Phys. Rev. Lett. in pres
"Electro-flux" effect in superconducting hybrid Aharonov-Bohm rings
We have extended the circuit theory of Andreev conductance [Phys.~Rev.~Lett.
{\bf 73}, 1420 (1994)] to diffusive superconducting hybrid structures that
contain an Aharonov-Bohm ring. The electrostatic potential distribution in the
system is predicted to be flux-dependent with a period of the superconducting
flux quantum . When at least one tunnel barrier is present, the
conductance of the system oscillates with the same period.Comment: 4 pages RevTex including three Postscript figures. Also available at
http://www.tn.tudelft.nl/tn/thssci.htm
Weak point disorder in strongly fluctuating flux-line liquids
We consider the effect of weak uncorrelated quenched disorder (point defects)
on a strongly fluctuating flux-line liquid. We use a hydrodynamic model which
is based on mapping the flux-line system onto a quantum liquid of relativistic
charged bosons in 2+1 dimensions [P. Benetatos and M. C. Marchetti, Phys. Rev.
B 64, 054518, (2001)]. In this model, flux lines are allowed to be arbitrarily
curved and can even form closed loops. Point defects can be scalar or polar. In
the latter case, the direction of their dipole moments can be random or
correlated. Within the Gaussian approximation of our hydrodynamic model, we
calculate disorder-induced corrections to the correlation functions of the
flux-line fields and the elastic moduli of the flux-line liquid. We find that
scalar disorder enhances loop nucleation, and polar (magnetic) defects decrease
the tilt modulus.Comment: 15 pages, submitted to Pramana-Journal of Physics for the special
volume on Vortex State Studie
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