245 research outputs found
Dimensional Crossover of the Dephasing Time in Disordered Mesoscopic Rings: From Diffusive through Ergodic to 0D Behavior
We analyze dephasing by electron interactions in a small disordered quasi-one
dimensional (1D) ring weakly coupled to leads, where we recently predicted a
crossover for the dephasing time \tPh(T) from diffusive or ergodic 1D
(\tPh^{-1} \propto T^{2/3}, T^{1}) to behavior (\tPh^{-1} \propto
T^{2}) as drops below the Thouless energy \ETh. We provide a detailed
derivation of our results, based on an influence functional for quantum Nyquist
noise, and calculate all leading and subleading terms of the dephasing time in
the three regimes. Explicitly taking into account the Pauli blocking of the
Fermi sea in the metal allows us to describe the regime on equal footing
as the others. The crossover to , predicted by Sivan, Imry and Aronov for
3D systems, has so far eluded experimental observation. We will show that for
T \ll \ETh, dephasing governs not only the -dependence for the smooth
part of the magnetoconductivity but also for the amplitude of the
Altshuler-Aronov-Spivak oscillations, which result only from electron paths
winding around the ring. This observation can be exploited to filter out and
eliminate contributions to dephasing from trajectories which do not wind around
the ring, which may tend to mask the behavior. Thus, the ring geometry
holds promise of finally observing the crossover to experimentally.Comment: in "Perspectives of Mesoscopic Physics - Dedicated to Yoseph Imry's
70th Birthday", edited by Amnon Aharony and Ora Entin-Wohlman (World
Scientific, 2010), chap. 20, p. 371-396, ISBN-13 978-981-4299-43-
Anderson localization transition with long-ranged hoppings : analysis of the strong multifractality regime in terms of weighted Levy sums
For Anderson tight-binding models in dimension with random on-site
energies and critical long-ranged hoppings decaying
typically as , we show that the strong multifractality
regime corresponding to small can be studied via the standard perturbation
theory for eigenvectors in quantum mechanics. The Inverse Participation Ratios
, which are the order parameters of Anderson transitions, can be
written in terms of weighted L\'evy sums of broadly distributed variables (as a
consequence of the presence of on-site random energies in the denominators of
the perturbation theory). We compute at leading order the typical and
disorder-averaged multifractal spectra and as a
function of . For , we obtain the non-vanishing limiting spectrum
as . For , this method
yields the same disorder-averaged spectrum of order as
obtained previously via the Levitov renormalization method by Mirlin and Evers
[Phys. Rev. B 62, 7920 (2000)]. In addition, it allows to compute explicitly
the typical spectrum, also of order , but with a different -dependence
for all . As a consequence, we find
that the corresponding singularity spectra and
differ even in the positive region , and vanish at
different values , in contrast to the standard
picture. We also obtain that the saddle value of the Legendre
transform reaches the termination point where
only in the limit .Comment: 13 pages, 2 figures, v2=final versio
Thermal noise and dephasing due to electron interactions in non-trivial geometries
We study Johnson-Nyquist noise in macroscopically inhomogeneous disordered
metals and give a microscopic derivation of the correlation function of the
scalar electric potentials in real space. Starting from the interacting
Hamiltonian for electrons in a metal and the random phase approximation, we
find a relation between the correlation function of the electric potentials and
the density fluctuations which is valid for arbitrary geometry and
dimensionality. We show that the potential fluctuations are proportional to the
solution of the diffusion equation, taken at zero frequency. As an example, we
consider networks of quasi-1D disordered wires and give an explicit expression
for the correlation function in a ring attached via arms to absorbing leads. We
use this result in order to develop a theory of dephasing by electronic noise
in multiply-connected systems.Comment: 9 pages, 6 figures (version submitted to PRB
Temperature operating mode of the CuBr+Ne+H2(HBr)-laser at change of pumping
The analysis of a temperature mode of the laser on copper bromide vapour using active additives of hydrogen (bromhydrogen) at change of pumping parameters has been carried out. It is shown that introduction of the optimal additive increases the discharge tube wall temperature from 620 up to 720 °С. The increase of wall temperature 50...60 °С more can occur at change of buffer gas pressure from 3,3 to 13,3 kPa, as well as at increase working capacity twice. It is stated that introduction of the additive raises pressure of working substance vapours in the active media of the laser of average diameter 6,7 Pa more due to interaction of bromine, bromhydrogen with copper atoms settled on the tube wall. The peculiarities of laser thermal mode at high frequencies of pulse sequences (up to 100 kHz) have been considered
A new approach to the treatment of Separatrix Chaos and its applications
We consider time-periodically perturbed 1D Hamiltonian systems possessing one or more separatrices. If the perturbation is weak, then the separatrix chaos is most developed when the perturbation frequency lies in the logarithmically small or moderate ranges: this corresponds to the involvement of resonance dynamics into the separatrix chaos. We develop a method matching the discrete chaotic dynamics of the separatrix map and the continuous regular dynamics of the resonance Hamiltonian. The method has allowed us to solve the long-standing problem of an accurate description of the maximum of the separatrix chaotic layer width as a function of the perturbation frequency. It has also allowed us to predict and describe
new phenomena including, in particular: (i) a drastic facilitation of the onset of global chaos between neighbouring separatrices, and (ii) a huge increase in the
size of the low-dimensional stochastic web
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