1,986 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
Quasilinear spin voltage profiles in spin thermoelectrics
Recent experiments show that spin thermoelectrics is a promising approach to
generate spin voltages. While spin chemical potentials are often limited to a
surface layer of the order of the spin diffusion length, we show that
thermoelectrically induced spin chemical potentials can extend much further in
itinerant ferromagnets with paramagnetic impurities. In some cases,
conservation laws, e.g., for a combination of spin and heat currents, give rise
to a linear spin voltage profile. More generally, we find quasilinear profiles
involving a spin thermoelectric length scale which far exceeds the spin
diffusion length.Comment: 4+ page
Anomalous Hall effect in a two dimensional electron gas with magnetic impurities
Magnetic impurities play an important role in many spintronics-related
materials. Motivated by this fact, we study the anomalous Hall effect in the
presence of magnetic impurities, focusing on two-dimensional electron systems
with Rashba spin-orbit coupling. We find a highly nonlinear dependence on the
impurity polarization, including possible sign changes. At small impurity
magnetizations, this is a consequence of the remarkable result that the linear
term is independent of the spin-orbit coupling strength. Near saturation of the
impurity spins, the anomalous Hall conductivity can be resonantly enhanced, due
to interference between potential and magnetic scattering.Comment: 5 pages, 3 figure
Combining Topological Hardware and Topological Software: Color Code Quantum Computing with Topological Superconductor Networks
We present a scalable architecture for fault-tolerant topological quantum
computation using networks of voltage-controlled Majorana Cooper pair boxes,
and topological color codes for error correction. Color codes have a set of
transversal gates which coincides with the set of topologically protected gates
in Majorana-based systems, namely the Clifford gates. In this way, we establish
color codes as providing a natural setting in which advantages offered by
topological hardware can be combined with those arising from topological
error-correcting software for full-fledged fault-tolerant quantum computing. We
provide a complete description of our architecture including the underlying
physical ingredients. We start by showing that in topological superconductor
networks, hexagonal cells can be employed to serve as physical qubits for
universal quantum computation, and present protocols for realizing
topologically protected Clifford gates. These hexagonal cell qubits allow for a
direct implementation of open-boundary color codes with ancilla-free syndrome
readout and logical -gates via magic state distillation. For concreteness,
we describe how the necessary operations can be implemented using networks of
Majorana Cooper pair boxes, and give a feasibility estimate for error
correction in this architecture. Our approach is motivated by nanowire-based
networks of topological superconductors, but could also be realized in
alternative settings such as quantum Hall-superconductor hybrids.Comment: 24 pages, 24 figure
General Localization Lengths for Two Interacting Particles in a Disordered Chain
The propagation of an interacting particle pair in a disordered chain is
characterized by a set of localization lengths which we define. The
localization lengths are computed by a new decimation algorithm and provide a
more comprehensive picture of the two-particle propagation. We find that the
interaction delocalizes predominantly the center-of-mass motion of the pair and
use our approach to propose a consistent interpretation of the discrepancies
between previous numerical results.Comment: 4 pages, 2 epsi figure
Electron Pair Resonance in the Coulomb Blockade
We study many-body corrections to the cotunneling current via a localized
state with energy at large bias voltages . We show that the
transfer of {\em electron pairs}, enabled by the Coulomb repulsion in the
localized level, results in ionization resonance peaks in the third derivative
of the current with respect to , centered at . Our
results predict the existence of previously unnoticed structure within
Coulomb-blockade diamonds.Comment: 5 pages, 4 figure
Localization Properties of Two Interacting Electrons in a Disordered Quasi One-Dimensional Potential
We study the transport properties of two electrons in a quasi one-dimensional
disordered wire. The electrons are subject to both, a disorder potential and a
short range two-body interaction. Using the approach developed by Iida et al. [
Ann. Phys. (N.Y.) 200 (1990) 219 ], the supersymmetry technique, and a suitable
truncation of Hilbert space, we work out the two-point correlation function in
the framework of a non-linear sigma model. We study the loop corrections to
arbitrary order. We obtain a remarkably simple and physically transparent
expression for the change of the localization length caused by the two-body
interaction.Comment: 10 page
Effect of noise for two interacting particles in a random potential
We investigated the effect of noise on propagation of two interacting
particles pairs in a quasi one--dimensional random potential. It is shown that
pair diffusion is strongly enhanced by short range interaction comparing with
the non--interacting case.Comment: 8 Latex pages + 3 postscript figures uu- compressed submitted to
Europhysics Letter
Quantal Brownian Motion - Dephasing and Dissipation
We analyze quantal Brownian motion in dimensions using the unified model
for diffusion localization and dissipation, and Feynman-Vernon formalism. At
high temperatures the propagator possess a Markovian property and we can write
down an equivalent Master equation. Unlike the case of the
Zwanzig-Caldeira-Leggett model, genuine quantum mechanical effects manifest
themselves due to the disordered nature of the environment. Using Wigner
picture of the dynamics we distinguish between two different mechanisms for
destruction of coherence. The analysis of dephasing is extended to the low
temperature regime by using a semiclassical strategy. Various results are
derived for ballistic, chaotic, diffusive, both ergodic and non-ergodic motion.
We also analyze loss of coherence at the limit of zero temperature and clarify
the limitations of the semiclassical approach. The condition for having
coherent effect due to scattering by low-frequency fluctuations is also pointed
out. It is interesting that the dephasing rate can be either larger or smaller
than the dissipation rate, depending on the physical circumstances.Comment: LaTex, 23 pages, 4 figures, published vesio
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