4,061 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
Current relaxation in nonlinear random media
We study the current relaxation of a wave packet in a nonlinear random sample
coupled to the continuum and show that the survival probability decays as . For intermediate times , the exponent
satisfies a scaling law where is
the nonlinearity strength and is the localization length of the
corresponding random system with . For and we find a universal decay with which is a signature of the
{\it nonlinearity-induced delocalization}. Experimental evidence should be
observable in coupled nonlinear optical waveguides.Comment: revised version, PRL in press, 4 pages, 4 figs (fig 3 with reduced
quality
Comment on "Quantum Decoherence in Disordered Mesoscopic Systems"
In a recent paper, Phys. Rev. Lett. 81, 1074 (1998), Golubev and Zaikin (GZ)
found that ``zero-point fluctuations of electrons'' contribute to the dephasing
rate extracted from the magnetoresistance. As a result, the dephasing rate
remains finite at zero temperature. GZ claimed that their results ``agree well
with the experimental data''. We point out that the GZ results are incompatible
with (i) conventional perturbation theory of the effects of interaction on weak
localization (WL), and (ii) with the available experimental data. More detailed
criticism of GZ findings can be found in cond-mat/9808053.Comment: 1 page, no figure
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
Chiral single-wall gold nanotubes
Based on first-principles calculations we show that gold atoms can form both
free-standing and tip-suspended chiral single-wall nanotubes composed of
helical atomic strands. Free-standing, infinite (5,5) tube is found to be
energetically the most favorable. While energetically less favorable, the
experimentally observed (5,3) tube stretching between two tips corresponds to a
local minimum in the string tension. Similarly, the (4,3) tube is predicted as
a favorable structure yet to be observed experimentally. Analysis of band
structure, charge density, and quantum ballistic conductance suggests that the
current on these wires is less chiral than expected, and there is no direct
correlation between the numbers of conduction channels and helical strands.Comment: Figures provided in eps forma
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
Coulomb Blockade of Tunneling between Disordered Conductors
We determine the zero-bias anomaly of the conductance of tunnel junctions by
an approach unifying the conventional Coulomb blockade theory for ultrasmall
junctions with the diffusive anomalies in disordered conductors. Both,
electron-electron interactions within the electrodes and electron-hole
interactions between the electrodes are taken into account nonperturbatively.
Explicit results are given for one- and two-dimensional junctions, and the
crossover to ultrasmall junctions is discussed.Comment: 4 pages, 1 figure. Final version published in Phys. Rev. Let
Dephasing time and magnetoresistance of two-dimensional electron gas in spatially modulated magnetic fields
The effect of a spatially modulated magnetic field on the weak localization
phenomenon in two-dimensional electron gas (2DEG) is studied. Both the
dephasing time and magnetoresistance are shown to reveal a nontrivial
behavior as functions of the characteristics of magnetic field profiles. The
magnetic field profiles with rather small spatial scales and modulation
amplitudes such that are characterized by the
dephasing rate . The increase in the flux value
results in a crossover to a standard linear dependence
. Applying an external homogeneous magnetic field
one can vary the local dephasing time in the system and affect the resulting
average transport characteristics. We have investigated the dependence of the
average resistance vs the field for some generic systems and predict a
possibility to observe a positive magnetoresistance at not too large
values. The resulting dependence of the resistance vs should reveal a peak
at the field values .Comment: 12 pages, 5 figure
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