269 research outputs found
Elastic theory of quantum Hall smectics: effects of disorder
We study the effect of disorder on quantum Hall smectics within the framework
of an elastic theory. Based on a renormalization group calculation, we derive
detailed results for the degrees of translational and orientational order of
the stripe pattern at zero temperature and carefully map out the disorder and
length-scale regimes in which the system effectively exhibits smectic, nematic,
or isotropic behavior. We show that disorder always leads to a finite density
of free dislocations and estimate the scale on which they begin to appear.Comment: 4 pages latex with 1 EPS figur
Non-universal ordering of spin and charge in stripe phases
We study the interplay of topological excitations in stripe phases: charge
dislocations, charge loops, and spin vortices. In two dimensions these defects
interact logarithmically on large distances. Using a renormalization-group
analysis in the Coulomb gas representation of these defects, we calculate the
phase diagram and the critical properties of the transitions. Depending on the
interaction parameters, spin and charge order can disappear at a single
transition or in a sequence of two transitions (spin-charge separation). These
transitions are non-universal with continuously varying critical exponents. We
also determine the nature of the points where three phases coexist.Comment: 4 pages, 3 figure
XY models with disorder and symmetry-breaking fields in two dimensions
The combined effect of disorder and symmetry-breaking fields on the
two-dimensional XY model is examined. The study includes disorder in the
interaction among spins in the form of random phase shifts as well as disorder
in the local orientation of the field. The phase diagrams are determined and
the properties of the various phases and phase transitions are calculated. We
use a renormalization group approach in the Coulomb gas representation of the
model. Our results differ from those obtained for special cases in previous
works. In particular, we find a changed topology of the phase diagram that is
composed of phases with long-range order, quasi-long-range order, and
short-range order. The discrepancies can be ascribed to a breakdown of the
fugacity expansion in the Coulomb gas representation.
Implications for physical systems such as planar Josephson junctions and the
faceting of crystal surfaces are discussed.Comment: 17 pages Latex with 5 eps figures, change: acknowledgment extende
Hall noise and transverse freezing in driven vortex lattices
We study driven vortices lattices in superconducting thin films. Above the
critical force we find two dynamical phase transitions at and
, which could be observed in simultaneous noise measurements of the
longitudinal and the Hall voltage. At there is a transition from plastic
flow to smectic flow where the voltage noise is isotropic (Hall noise =
longitudinal noise) and there is a peak in the differential resistance. At
there is a sharp transition to a frozen transverse solid where the Hall
noise falls down abruptly and vortex motion is localized in the transverse
direction.Comment: 4 pages, 3 figure
Nonequilibrium dislocation dynamics and instability of driven vortex lattices in two dimensions
We consider dislocations in a vortex lattice that is driven in a
two-dimensional superconductor with random impurities. The structure and
dynamics of dislocations is studied in this genuine nonequilibrium situation on
the basis of a coarse-grained equation of motion for the displacement field.
The presence of dislocations leads to a characteristic anisotropic distortion
of the vortex density that is controlled by a Kardar-Parisi-Zhang nonlinearity
in the coarse-grained equation of motion. This nonlinearity also implies a
screening of the interaction between dislocations and thereby an instability of
the vortex lattice to the proliferation of free dislocations.Comment: published version with minor correction
Nonequilibrium Phase Transitions of Vortex Matter in Three-Dimensional Layered Superconductors
Large-scale simulations on three-dimensional (3D) frustrated anisotropic XY
model have been performed to study the nonequilibrium phase transitions of
vortex matter in weak random pinning potential in layered superconductors. The
first-order phase transition from the moving Bragg glass to the moving smectic
is clarified, based on thermodynamic quantities. A washboard noise is observed
in the moving Bragg glass in 3D simulations for the first time. It is found
that the activation of the vortex loops play the dominant role in the dynamical
melting at high drive.Comment: 3 pages,5 figure
Quantum teleportation using active feed-forward between two Canary Islands
Quantum teleportation [1] is a quintessential prerequisite of many quantum
information processing protocols [2-4]. By using quantum teleportation, one can
circumvent the no-cloning theorem [5] and faithfully transfer unknown quantum
states to a party whose location is even unknown over arbitrary distances. Ever
since the first experimental demonstrations of quantum teleportation of
independent qubits [6] and of squeezed states [7], researchers have
progressively extended the communication distance in teleportation, usually
without active feed-forward of the classical Bell-state measurement result
which is an essential ingredient in future applications such as communication
between quantum computers. Here we report the first long-distance quantum
teleportation experiment with active feed-forward in real time. The experiment
employed two optical links, quantum and classical, over 143 km free space
between the two Canary Islands of La Palma and Tenerife. To achieve this, the
experiment had to employ novel techniques such as a frequency-uncorrelated
polarization-entangled photon pair source, ultra-low-noise single-photon
detectors, and entanglement-assisted clock synchronization. The average
teleported state fidelity was well beyond the classical limit of 2/3.
Furthermore, we confirmed the quality of the quantum teleportation procedure
(without feed-forward) by complete quantum process tomography. Our experiment
confirms the maturity and applicability of the involved technologies in
real-world scenarios, and is a milestone towards future satellite-based quantum
teleportation
DebrisInterMixing-2.3: a finite volume solver for three-dimensional debris-flow simulations with two calibration parameters. Part 2: Model validation with experiments
Here, we present validation tests of the fluid dynamic solver presented in von Boetticher et al. (2016), simulating both laboratory-scale and large-scale debris-flow experiments. The new solver combines a Coulomb viscoplastic rheological model with a Herschel-Bulkley model based on material properties and rheological characteristics of the analyzed debris flow. For the selected experiments in this study, all necessary material properties were known - the content of sand, clay (including its mineral composition) and gravel as well as the water content and the angle of repose of the gravel. Given these properties, two model parameters are sufficient for calibration, and a range of experiments with different material compositions can be reproduced by the model without recalibration. One calibration parameter, the Herschel-Bulkley exponent, was kept constant for all simulations. The model validation focuses on different case studies illustrating the sensitivity of debris flows to water and clay content, channel curvature, channel roughness and the angle of repose. We characterize the accuracy of the model using experimental observations of flow head positions, front velocities, run-out patterns and basal pressures.Peer ReviewedPostprint (published version
Renormalization group approach to layered superconductors
A renormalization group theory for a system consisting of coupled
superconducting layers as a model for typical high-temperature superconducters
is developed. In a first step the electromagnetic interaction over infinitely
many layers is taken into account, but the Josephson coupling is neglected. In
this case the corrections to two-dimensional behavior due to the presence of
the other layers are very small. Next, renormalization group equations for a
layered system with very strong Josephson coupling are derived, taking into
account only the smallest possible Josephson vortex loops. The applicability of
these two limiting cases to typical high-temperature superconductors is
discussed. Finally, it is argued that the original renormalization group
approach by Kosterlitz is not applicable to a layered system with intermediate
Josephson coupling.Comment: RevTeX, 15 pages, 4 figures can be obtained from the author by
conventional mail; accepted for publication in Phys. Rev.
Delocalization in Coupled Luttinger Liquids with Impurities
We study effects of quenched disorder on coupled two-dimensional arrays of
Luttinger liquids (LL) as a model for stripes in high-T_c compounds. In the
framework of a renormalization-group analysis, we find that weak inter-LL
charge-density-wave couplings are always irrelevant as opposed to the pure
system. By varying either disorder strength, intra- or inter-LL interactions,
the system can undergo a delocalization transition between an insulator and a
novel strongly anisotropic metallic state with LL-like transport. This state is
characterized by short-ranged charge-density-wave order, the superconducting
order is quasi long-ranged along the stripes and short-ranged in the
transversal direction.Comment: 6 pages, 5 figures, substantially extended and revised versio
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