965 research outputs found
Glass phases of flux lattices in layered superconductors
We study a flux lattice which is parallel to superconducting layers, allowing
for dislocations and for disorder of both short wavelength and long wavelength.
We find that the long wavelength disorder has a significant effect on the phase
diagram -- it produces a first order transition within the Bragg glass phase
and leads to melting at strong disorder. This then allows a Friedel scenario of
2D superconductivity.Comment: 5 pages, 1 eps figure, Revte
A study of the Big Brother Association of Boston, 1949 and 1950.
Thesis (M.S.)--Boston University
N.B.: Page 61 missing from this thesis. Only one physical copy was available
Antiferromagnetic domain walls in lightly doped layered cuprates
Recent ESR data shows rotation of the antiferromagnetic (AF) easy axis in
lightly doped layered cuprates upon lowering the temperature. We account for
the ESR data and show that it has significant implications on spin and charge
ordering according to the following scenario: In the high temperature phase AF
domain walls coincide with (110) twin boundaries of an orthorhombic phase. A
magnetic field leads to annihilation of neighboring domain walls resulting in
antiphase boundaries. The latter are spin carriers, form ferromagnetic lines
and may become charged in the doped system. However, hole ordering at low
temperatures favors the (100) orientation, inducing a pi/4 rotation in the AF
easy axis. The latter phase has twin boundaries and AF domain walls in (100)
planes.Comment: 4 pages, 3 figures (1 eps). v2: no change in content, Tex shadow
problem cleare
Disorder Induced Transitions in Layered Coulomb Gases and Superconductors
A 3D layered system of charges with logarithmic interaction parallel to the
layers and random dipoles is studied via a novel variational method and an
energy rationale which reproduce the known phase diagram for a single layer.
Increasing interlayer coupling leads to successive transitions in which charge
rods correlated in N>1 neighboring layers are nucleated by weaker disorder. For
layered superconductors in the limit of only magnetic interlayer coupling, the
method predicts and locates a disorder-induced defect-unbinding transition in
the flux lattice. While N=1 charges dominate there, N>1 disorder induced defect
rods are predicted for multi-layer superconductors.Comment: 4 pages, 2 figures, RevTe
Single vortex fluctuations in a superconducting chip as generating dephasing and spin flips in cold atom traps
We study trapping of a cold atom by a single vortex line in an extreme type
II superconducting chip, allowing for pinning and friction. We evaluate the
atom's spin flip rate and its dephasing due to the vortex fluctuations in
equilibrium and find that they decay rapidly when the distance to the vortex
exceeds the magnetic penetration length. We find that there are special spin
orientations, depending on the spin location relative to the vortex, at which
spin dephasing is considerably reduced while perpendicular directions have a
reduced spin flip rate. We also show that the vortex must be perpendicular to
the surface for a general shape vortex.Comment: 6 pages, 4 figure
Interference in presence of Dissipation
We study a particle on a ring in presence of various dissipative
environments. We develop and solve a variational scheme assuming low frequency
dominance. We analyze our solution within a renormalization group (RG) scheme
to all orders which reproduces a 2 loop RG for the Caldeira-Legget environment.
In the latter case the Aharonov-Bohm (AB) oscillation amplitude is exponential
in -R^2 where R is the ring's radius. For either a charge or an electric dipole
coupled to a dirty metal we find that the metal induces dissipation, however
the AB amplitude is ~ R^{-2} for large R, as for free particles. Cold atoms
with a large electric dipole may show a crossover between these two behaviors.Comment: 5 pages, added motivations and reference
Spontaneous magnetization and Hall effect in superconductors with broken time-reversal symmetry
Broken time reversal symmetry (BTRS) in d wave superconductors is studied and
is shown to yield current carrying surface states. The corresponding
spontaneous magnetization is temperature independent near the critical
temperature Tc for weak BTRS, in accord with recent data. For strong BTRS and
thin films we expect a temperature dependent spontaneous magnetization with a
paramagnetic anomaly near Tc. The Hall conductance is found to vanish at zero
wavevector q and finite frequency w, however at finite q,w it has an unusual
structure.Comment: 7 pages, 1 eps figure, Europhysics Letters (in press
Decoherence of a particle in a ring
We consider a particle coupled to a dissipative environment and derive a
perturbative formula for the dephasing rate based on the purity of the reduced
probability matrix. We apply this formula to the problem of a particle on a
ring, that interacts with a dirty metal environment. At low but finite
temperatures we find a dephasing rate , and identify dephasing
lengths for large and for small rings. These findings shed light on recent
Monte Carlo data regarding the effective mass of the particle. At zero
temperature we find that spatial fluctuations suppress the possibility of
having a power law decay of coherence.Comment: 5 pages, 1 figure, proofed version to be published in EP
Second magnetization peak in flux lattices: the decoupling scenario
The second peak phenomena of flux lattices in layered superconductors is
described in terms of a disorder induced layer decoupling transition. For weak
disorder the tilt mudulus undergoes an apparent discontinuity which leads to an
enhanced critical current and reduced domain size in the decoupled phase. The
Josephson plasma frequency is reduced by decoupling and by Josephson glass
pinning; in the liquid phase it varies as 1/[BT(T+T_0)] where T is temperature,
B is field and T_0 is the disorder dependent temperature of the multicritical
point.Comment: 5 pages, 1 eps figure, Revtex. Minor changes, new reference
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