6 research outputs found
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
Dephasing of a particle in a dissipative environment
The motion of a particle in a ring of length L is influenced by a dirty metal
environment whose fluctuations are characterized by a short correlation
distance . We analyze the induced decoherence process, and compare
the results with those obtained in the opposing Caldeira-Leggett limit (). A proper definition of the dephasing factor that does not depend on a
vague semiclassical picture is employed. Some recent Monte-Carlo results about
the effect of finite temperatures on "mass renormalization" in this system are
illuminated.Comment: 18 pages, 2 figures, some textual improvements, to be published in
JP
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
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
Geometry dependent dephasing in small metallic wires
Temperature dependent weak localization is measured in metallic nanowires in
a previously unexplored size regime down to width nm. The dephasing time,
, shows a low temperature dependence close to quasi-1D
theoretical expectations () in the narrowest wires,
but exhibits a relative saturation as for wide samples of the same
material, as observed previously. As only sample geometry is varied to exhibit
both suppression and divergence of , this finding provides a new
constraint on models of dephasing phenomena.Comment: 6 pages, 3 figure
Magnetolocalization in disordered quantum wires
The magnetic field dependent localization in a disordered quantum wire is
considered nonperturbatively.
An increase of an averaged localization length with the magnetic field is
found, saturating at twice its value without magnetic field.
The crossover behavior is shown to be governed both in the weak and strong
localization regime by the magnetic diffusion length L_B. This function is
derived analytically in closed form as a function of the ratio of the mean free
path l, the wire thickness W, and the magnetic length l_B for a two-dimensional
wire with specular boundary conditions, as well as for a parabolic wire. The
applicability of the analytical formulas to resistance measurements in the
strong localization regime is discussed. A comparison with recent experimental
results on magnetolocalization is included.Comment: 22 pages, RevTe