3,129 research outputs found
Microwave-Induced Dephasing in One-Dimensional Metal Wires
We report on the effect of monochromatic microwave (MW) radiation on the weak
localization corrections to the conductivity of quasi-one-dimensional (1D)
silver wires. Due to the improved electron cooling in the wires, the MW-induced
dephasing was observed without a concomitant overheating of electrons over wide
ranges of the MW power and frequency . The observed dependences of
the conductivity and MW-induced dephasing rate on and are in
agreement with the theory by Altshuler, Aronov, and Khmelnitsky \cite{Alt81}.
Our results suggest that in the low-temperature experiments with 1D wires,
saturation of the temperature dependence of the dephasing time can be caused by
an MW electromagnetic noise with a sub-pW power.Comment: 4 pages with 4 figures, paper revised, accepted by Phys Rev Let
Anderson localisation in tight-binding models with flat bands
We consider the effect of weak disorder on eigenstates in a special class of
tight-binding models. Models in this class have short-range hopping on periodic
lattices; their defining feature is that the clean systems have some energy
bands that are dispersionless throughout the Brillouin zone. We show that
states derived from these flat bands are generically critical in the presence
of weak disorder, being neither Anderson localised nor spatially extended.
Further, we establish a mapping between this localisation problem and the one
of resonances in random impedance networks, which previous work has suggested
are also critical. Our conclusions are illustrated using numerical results for
a two-dimensional lattice, known as the square lattice with crossings or the
planar pyrochlore lattice.Comment: 5 pages, 3 figures, as published (this version includes minor
corrections
Quantum coherence in a ferromagnetic metal: time-dependent conductance fluctuations
Quantum coherence of electrons in ferromagnetic metals is difficult to assess
experimentally. We report the first measurements of time-dependent universal
conductance fluctuations in ferromagnetic metal (NiFe)
nanostructures as a function of temperature and magnetic field strength and
orientation. We find that the cooperon contribution to this quantum correction
is suppressed, and that domain wall motion can be a source of
coherence-enhanced conductance fluctuations. The fluctuations are more strongly
temperature dependent than those in normal metals, hinting that an unusual
dephasing mechanism may be at work.Comment: 5 pages, 4 figure
Weak localization effect on thermomagnetic phenomena
The quantum transport equation (QTE) is extended to study weak localization
(WL) effects on galvanomagnetic and thermomagnetic phenomena. QTE has many
advantages over the linear response method (LRM): (i) particle-hole asymmetry
which is necessary for the Hall effect is taken into account by the
nonequilibrium distribution function, while LRM requires expansion near the
Fermi surface, (ii) when calculating response to the temperature gradient, the
problem of WL correction to the heat current operator is avoided, (iii)
magnetic field is directly introduced to QTE, while the LRM deals with the
vector potential and and special attention should be paid to maintain gauge
invariance, e.g. when calculating the Nernst effect the heat current operator
should be modified to include the external magnetic field. We reproduce in a
very compact form known results for the conductivity, the Hall and the
thermoelectric effects and then we study our main problem, WL correction to the
Nernst coefficient (transverse thermopower).Comment: 20 pages 2 figure
Universal conductance fluctuations in Dirac materials in the presence of long-range disorder
We study quantum transport in Dirac materials with a single fermionic Dirac
cone (strong topological insulators and graphene in the absence of intervalley
coupling) in the presence of non-Gaussian long-range disorder. We show, by
directly calculating numerically the conductance fluctuations, that in the
limit of very large system size and disorder strength, quantum transport
becomes universal. However, a systematic deviation away from universality is
obtained for realistic system parameters. By comparing our results to existing
experimental data on 1/f noise, we suggest that many of the graphene samples
studied to date are in a non-universal crossover regime of conductance
fluctuations.Comment: 5 pages, 3 figures. Published versio
Level correlations in integrable systems
We derive a simple analytical expression for the level correlation function
of an integrable system. It accounts for both the lack of correlations at
smaller energy scales and for global rigidity (level number conservation) at
larger scales. We apply our results to a rectangle with incommensurate sides
and show that they are in excellent agreement with the limiting cases
established in the semiclassical theory of level rigidity.Comment: 5 page
Critical level statistics and anomalously localized states at the Anderson transition
We study the level-spacing distribution function at the Anderson
transition by paying attention to anomalously localized states (ALS) which
contribute to statistical properties at the critical point. It is found that
the distribution for level pairs of ALS coincides with that for pairs of
typical multifractal states. This implies that ALS do not affect the shape of
the critical level-spacing distribution function. We also show that the
insensitivity of to ALS is a consequence of multifractality in tail
structures of ALS.Comment: 8 pages, 5 figure
Interaction effects and phase relaxation in disordered systems
This paper is intended to demonstrate that there is no need to revise the
existing theory of the transport properties of disordered conductors in the
so-called weak localization regime. In particular, we demonstrate explicitly
that recent attempts to justify theoretically that the dephasing rate
(extracted from the magnetoresistance) remains finite at zero temperature are
based on the profoundly incorrect calculation. This demonstration is based on a
straightforward evaluation of the effect of the electron-electron interaction
on the weak localization correction to the conductivity of disordered metals.
Using well-controlled perturbation theory with the inverse conductance as
the small parameter, we show that this effect consists of two contributions.
First contribution comes from the processes with energy transfer smaller than
the temperature. This contribution is responsible for setting the energy scale
for the magnetoresistance. The second contribution originates from the virtual
processes with energy transfer larger than the temperature. It is shown that
the latter processes have nothing to do with the dephasing, but rather manifest
the second order (in ) correction to the conductance. This correction is
calculated for the first time. The paper also contains a brief review of the
existing experiments on the dephasing of electrons in disordered conductors and
an extended qualitative discussion of the quantum corrections to the
conductivity and to the density of electronic states in the weak localization
regime.Comment: 34 pages, 13 .eps figure
Non-linear effects and dephasing in disordered electron systems
The calculation of the dephasing time in electron systems is presented. By
means of the Keldysh formalism we discuss in a unifying way both weak
localization and interaction effects in disordered systems. This allows us to
show how dephasing arises both in the particle-particle channel (weak
localization) and in the particle-hole channel (interaction effect). First we
discuss dephasing by an external field. Besides reviewing previous work on how
an external oscillating field suppresses the weak localization correction, we
derive a new expression for the effect of a field on the interaction
correction. We find that the latter may be suppressed by a static electric
field, in contrast to weak localization. We then consider dephasing due to
inelastic scattering. The ambiguities involved in the definition of the
dephasing time are clarified by directly comparing the diagrammatic approach
with the path-integral approach. We show that different dephasing times appear
in the particle-particle and particle-hole channels. Finally we comment on
recent experiments.Comment: 28 pages, 6 figures (14ps-files
Transport of interacting electrons in arrays of quantum dots and diffusive wires
We develop a detailed theoretical investigation of the effect of Coulomb
interaction on electron transport in arrays of chaotic quantum dots and
diffusive metallic wires. Employing the real time path integral technique we
formulate a new Langevin-type of approach which exploits a direct relation
between shot noise and interaction effects in mesoscopic conductors. With the
aid of this approach we establish a general expression for the Fano factor of
1D quantum dot arrays and derive a complete formula for the interaction
correction to the current which embraces all perturbative results previously
obtained for various quasi-0D and quasi-1D disordered conductors and extends
these results to yet unexplored regimes.Comment: 12 pages, 2 figure
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