36 research outputs found
Asymptotic formulas for probabilities of large deviations of ladder heights
Asymptotic formulas for large-deviation probabilities of a ladder height in a random
walk generated by a sequence of sums of i.i.d. random variables are deduced.
Two cases are considered:
a) the distribution F(x) of summands is normal with a zero mean.
b) F(x) belongs to the domain of the normal attraction of a stable law with
the exponent 0 < α < 1.
The method of Laplace transforms is applied in proofs
Anomalous crossover between thermal and shot noise in macroscopic diffusive conductors
We predict the existence of an anomalous crossover between thermal and shot
noise in macroscopic diffusive conductors. We first show that, besides thermal
noise, these systems may also exhibit shot noise due to fluctuations of the
total number of carriers in the system. Then we show that at increasing
currents the crossover between the two noise behaviors is anomalous, in the
sense that the low frequency current spectral density displays a region with a
superlinear dependence on the current up to a cubic law. The anomaly is due to
the non-trivial coupling in the presence of the long range Coulomb interaction
among the three time scales relevant to the phenomenon, namely, diffusion,
transit and dielectric relaxation time.Comment: 4 pages, 2 figure
Shot Noise at High Temperatures
We consider the possibility of measuring non-equilibrium properties of the
current correlation functions at high temperatures (and small bias). Through
the example of the third cumulant of the current () we demonstrate
that odd order correlation functions represent non-equilibrium physics even at
small external bias and high temperatures. We calculate for a quasi-one-dimensional diffusive constriction. We calculate the
scaling function in two regimes: when the scattering processes are purely
elastic and when the inelastic electron-electron scattering is strong. In both
cases we find that interpolates between two constants. In the low (high)
temperature limit is strongly (weakly) enhanced (suppressed) by the
electron-electron scattering.Comment: 11 pages 4 fig. submitted to Phys. Rev.
Theory of Interaction Effects in N-S Junctions out of Equilibrium
We consider a normal metal - superconductor (N-S) junction in the regime,
when electrons in the normal metal are driven out of equilibrium. We show that
the non-equilibrium fluctuations of the electron density in the N-layer cause
the fluctuations of the phase of the order parameter in the S-layer. As a
result, the density of states in the superconductor deviates from the BCS form,
most notably the density of states in the gap becomes finite. This effect can
be viewed as a result of the time reversal symmetry breaking due to the
non-equilibrium, and can be described in terms of a low energy collective mode
of the junction, which couples normal currents in N-layer and supercurrents.
This mode is analogous to the Schmid-Sch\"{o}n mode. To interpret their
measurements of the tunneling current, Pothier {\em et. al} [Phys. Rev. Lett.
{\bf 79}, 3490 (1997)] had to assume that the energy relaxation rate in the
normal metal is surprisingly high. The broadening of the BCS singularity of the
density of states in the S-layer manifest itself similarly to the broadening of
the distribution function. Mechanism suggested here can be a possible
explanation of this experimental puzzle. We also propose an independent
experiment to test our explanation.Comment: 16 pages, 2 .eps figure
Outlets of 2D invasion percolation and multiple-armed incipient infinite clusters
We study invasion percolation in two dimensions, focusing on properties of
the outlets of the invasion and their relation to critical percolation and to
incipient infinite clusters (IIC's). First we compute the exact decay rate of
the distribution of both the weight of the kth outlet and the volume of the kth
pond. Next we prove bounds for all moments of the distribution of the number of
outlets in an annulus. This result leads to almost sure bounds for the number
of outlets in a box B(2^n) and for the decay rate of the weight of the kth
outlet to p_c. We then prove existence of multiple-armed IIC measures for any
number of arms and for any color sequence which is alternating or
monochromatic. We use these measures to study the invaded region near outlets
and near edges in the invasion backbone far from the origin.Comment: 38 pages, 10 figures, added a thorough sketch of the proof of
existence of IIC's with alternating or monochromatic arms (with some
generalizations
Electron transport through interacting quantum dots
We present a detailed theoretical investigation of the effect of Coulomb
interactions on electron transport through quantum dots and double barrier
structures connected to a voltage source via an arbitrary linear impedance.
Combining real time path integral techniques with the scattering matrix
approach we derive the effective action and evaluate the current-voltage
characteristics of quantum dots at sufficiently large conductances. Our
analysis reveals a reach variety of different regimes which we specify in
details for the case of chaotic quantum dots. At sufficiently low energies the
interaction correction to the current depends logarithmically on temperature
and voltage. We identify two different logarithmic regimes with the crossover
between them occurring at energies of order of the inverse dwell time of
electrons in the dot. We also analyze the frequency-dependent shot noise in
chaotic quantum dots and elucidate its direct relation to interaction effects
in mesoscopic electron transport.Comment: 21 pages, 4 figures. References added, discussion slightly extende
On the self-consistent spin-wave theory of layered Heisenberg magnets
The versions of the self-consistent spin-wave theories (SSWT) of
two-dimensional (2D) Heisenberg ferro- and antiferromagnets with a weak
interlayer coupling and/or magnetic anisotropy, that are based on the
non-linear Dyson-Maleev, Schwinger, and combined boson-pseudofermion
representations, are analyzed. Analytical results for the temperature
dependences of (sublattice) magnetization and short-range order parameter, and
the critical points are obtained. The influence of external magnetic field is
considered. Fluctuation corrections to SSWT are calculated within a
random-phase approximation which takes into account correctly leading and
next-leading logarithmic singularities. These corrections are demonstrated to
improve radically the agreement with experimental data on layered perovskites
and other systems. Thus an account of these fluctuations provides a
quantitative theory of layered magnets.Comment: 46 pages, RevTeX, 7 figure
On limit theorems for continued fractions
It is shown that for sums of functionals of digits in continued fraction
expansion the Kolmogorov-Feller weak laws of large numbers and the
Khinchine-L\'evy-Feller-Raikov characterization of the domain of attraction of
the normal law hold.Comment: 16 page
Evanescent wave transport and shot noise in graphene: ballistic regime and effect of disorder
We have investigated electrical transport and shot noise in graphene field
effect devices. In large width over length ratio graphene strips, we have
measured shot noise at low frequency ( = 600--850 MHz) in the temperature
range of 4.2--30 K. We observe a minimum conductivity of
and a finite and gate dependent Fano factor reaching the universal value of 1/3
at the Dirac point, i.e. where the density of states vanishes. These findings
are in good agreement with the theory describing that transport at the Dirac
point should occur via evanescent waves in perfect graphene samples with large
. Moreover, we show and discuss how disorder and non-parallel leads affect
both conductivity and shot noise.Comment: Extended version (19 pages, 10 figures) of Phys. Rev. Lett. 100,
196802 (2008). Additional data on the effect of disorder and non-parallel
leads. Submitted for publication in Journal of Low Temperature Physics for
the Proceedings of the International Symposium on Quantum Phenomena and
Devices at Low Temperatures (ULTI 2008), Espoo, Finlan