957 research outputs found
U(1) symmetry breaking in one-dimensional Mott insulator studied by the Density Matrix Renormalization Group method
A new type of external fields violating the particle number preservation is
studied in one-dimensional strongly correlated systems by the Density Matrix
Renormalization Group method. Due to the U(1) symmetry breaking, the ground
state has fluctuation of the total particle number, which implies injection of
electrons and holes from out of the chain. This charge fluctuation can be
relevant even at half-filling because the particle-hole symmetry is preserved
with the finite effective field. In addition, we discuss a quantum phase
transition obtained by considering the symmetry-breaking fields as a mean field
of interchain-hopping.Comment: 7 pages, 4 figure
Vortex Dynamics in Ferromagnetic Superconductors: Vortex Clusters, Domain Walls and Enhanced Viscosity
We demonstrate that there is a long-range vortex-vortex attraction in
ferromagnetic superconductors due to polarization of the magnetic moments.
Vortex clusters are then stabilized in the ground state for low vortex
densities. The motion of vortex clusters driven by the Lorentz force excites
magnons. This regime becomes unstable at a threshold velocity above which
domain walls are generated for slow relaxation of the magnetic moments and the
vortex configuration becomes modulated. This dynamics of vortices and magnetic
moments can be probed by transport measurements.Comment: 6 pages and 3 figure
Anisotropy and directional pinning in YBaCuO with BaZrO3 nanorods
Measurements of anisotropic transport properties (dc and high-frequency
regime) of driven vortex matter in YBaCuO with elongated
strong-pinning sites (c-axis aligned, self-assembled BaZrO nanorods) are
used to demonstrate that the effective-mass angular scaling takes place only in
intrinsic physical quantities (flux-flow resistivity), and not in
pinning-related Labusch parameter and critical currents. Comparison of the
dynamics at different time scales shows evidence for a transition of the vortex
matter toward a Mott phase, driven by the presence of nanorods. The strong
pinning in dc arises partially from a dynamic effect.Comment: 4 pages, 4 figures. Accepted for publication on Applied Physics
Letters. With respect to v1: changed title, slightly shortene
Incoherent multiple Andreev reflection in an array of SNS junctions
Last years many interesting effects related to incoherent MAR have been
experimentally found, but only few of them were theoretically explained. It was
shown, for example, that if the voltage at the edges of a linear array is
then subgarmonic structures in the current -voltage characteristics appear not
only at usual for nonstationary Josephson effect positions, ,
where is integer, but also at voltages other than . A step towards
description of electron transport in a dirty array of SNS junctions is done in
this letter. It is shown that subgarmonic structures may indeed appear at
``unusual'' voltages
Mott transition and superconductivity in the strongly correlated organic superconductor -(BEDT-TTF)Cu[N(CN)Br
The magnetic field effect on the phase diagram of the organic Mott system
-(BEDT-TTF)Cu[N(CN)]Br in which the bandwidth was tuned by
the substitution of deuterated molecules was studied by means of the
resistivity measurements performed in magnetic fields. The lower critical point
of the first-order Mott transition, which ended on the upper critical field
-temperature plane of the superconductivity, was determined
experimentally in addition to the previously observed upper critical end point.
The lower critical end point moved to a lower temperature with the suppression
of in magnetic fields and the Mott transition recognized so far as
the -shaped curve reached 0 when in the end.Comment: 5 pages, 4 figure
Diamagnetism and flux creep in bilayer exciton superfluids
We discuss the diamagnetism induced in an isolated quantum Hall bilayer with
total filling factor one by an in-plane magnetic field. This is a signature of
counterflow superfluidity in these systems. We calculate magnetically induced
currents in the presence of pinned vortices nucleated by charge disorder, and
predict a history-dependent diamagnetism that could persist on laboratory
timescales. For current samples we find that the maximum in-plane moment is
small, but with stronger tunneling the moments would be measurable using torque
magnetometry. Such experiments would allow the persistent currents of a
counterflow superfluid to be observed in an electrically isolated bilayer.Comment: 8 pages, 2 figures. v2: updated to accepted version, extended
presentatio
Tunneling spectra for ()-wave superconductors versus tunneling spectra for ()-wave superconductors
The tunneling conductance spectra of a normal metal / insulator / singlet
superconductor is calculated from the reflection amplitudes using the
Blonder-Tinkham-Klapwijk (BTK) formulation. The pairing symmetry of the
superconductor is assumed to be , or . It
is found that in the ()-wave case there is a well defined
conductance peak in the conductance spectra, in the amplitude of the secondary
s-wave component. In the ()-wave case the tunneling
conductance has residual values within the gap, due to the formation of bound
states. The bound state energies depend on the angle of the incident
quasiparticles, and also on the boundary orientation. On the basis of this
observation an electron focusing experiment is proposed to probe the
()-wave state.Comment: 17 pages with 9 figure
High-field vortices in Josephson junctions with alternating critical current density
We study long Josephson junctions with the critical current density
alternating along the junction. New equilibrium states, which we call the field
synchronized or FS states, are shown to exist if the applied field is from
narrow intervals centered around equidistant series of resonant fields, .
The values of are much higher than the flux penetration field, . The
flux per period of the alternating critical current density, , is fixed
for each of the FS states. In the -th FS state the value of is
equal to an integer amount of flux quanta, . Two types of
single Josephson vortices carrying fluxes or/and can exist
in the FS states. Specific stepwise resonances in the current-voltage
characteristics are caused by periodic motion of these vortices between the
edges of the junction.Comment: 4 pages, 5 figure
Langevin Dynamics of the vortex matter two-stage melting transition in Bi_2Sr_2CaCu_2O in the presence of straight and of tilted columnar defects
In this paper we use London Langevin molecular dynamics simulations to
investigate the vortex matter melting transition in the highly anisotropic
high-temperature superconductor material Bi_2Sr_2CaCu_2O in the
presence of low concentration of columnar defects (CDs). We reproduce with
further details our previous results obtained by using Multilevel Monte Carlo
simulations that showed that the melting of the nanocrystalline vortex matter
occurs in two stages: a first stage melting into nanoliquid vortex matter and a
second stage delocalization transition into a homogeneous liquid. Furthermore,
we report on new dynamical measurements in the presence of a current that
identifies clearly the irreversibility line and the second stage delocalization
transition. In addition to CDs aligned along the c-axis we also simulate the
case of tilted CDs which are aligned at an angle with respect to the applied
magnetic field. Results for CDs tilted by with respect to c-axis
show that the locations of the melting and delocalization transitions are not
affected by the tilt when the ratio of flux lines to CDs remains constant. On
the other hand we argue that some dynamical properties and in particular the
position of the irreversibility line should be affected.Comment: 13 pages, 11 figure
Intrinsic Josephson Effect and Violation of the Josephson Relation in Layered Superconductors
Equations describing the resistive state of a layered superconductor with
anisotropic pairing are derived. The similarity with a stack of Josephson
junctions is found at small voltages only, when current density in the
direction perpendicular to the layers can be interpreted as a sum of the
Josephson superconducting, the Ohmic dissipative and the interference currents.
In the spatially uniform state differential conductivity at higher voltages
becomes negative. Nonuniformity of the current distribution generates the
branch imbalance and violates the Josephson relation between frequency and
voltage.Comment: 11 pages, no figures, revtex, to be published in Phys. Rev. Let
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