9,581 research outputs found
Point Charge Self-Energy in the General Relativity
Singularities in the metric of the classical solutions to the Einstein
equations (Schwarzschild, Kerr, Reissner -- Nordstr\"om and Kerr -- Newman
solutions) lead to appearance of generalized functions in the Einstein tensor
that are not usually taken into consideration. The generalized functions can be
of a more complex nature than the Dirac \d-function. To study them, a
technique has been used based on a limiting solution sequence. The solutions
are shown to satisfy the Einstein equations everywhere, if the energy-momentum
tensor has a relevant singular addition of non-electromagnetic origin. When the
addition is included, the total energy proves finite and equal to , while
for the Kerr and Kerr--Newman solutions the angular momentum is .
As the Reissner--Nordstr\"om and Kerr--Newman solutions correspond to the point
charge in the classical electrodynamics, the result obtained allows us to view
the point charge self-energy divergence problem in a new fashion.Comment: VI Fridmann Seminar, France, Corsica, Corgeze, 2004, LaTeX, 6 pages,
2 fige
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
Irreversibility on the Level of Single-Electron Tunneling
We present a low-temperature experimental test of the fluctuation theorem for
electron transport through a double quantum dot. The rare entropy-consuming
system trajectories are detected in the form of single charges flowing against
the source-drain bias by using time-resolved charge detection with a quantum
point contact. We find that these trajectories appear with a frequency that
agrees with the theoretical predictions even under strong nonequilibrium
conditions, when the finite bandwidth of the charge detection is taken into
account
Nonequilibrium phenomena in multiple normal-superconducting tunnel heterostructures
Using the nonequilibrium theory of superconductivity with the tunnel
Hamiltonian, we consider a mesoscopic NISINISIN heterostructure, i.e., a
structure consisting of five intermittent normal-metal (N) and superconducting
(S) regions separated by insulating tunnel barriers (I). Applying the bias
voltage between the outer normal electrodes one can drive the central N island
very far from equilibrium. Depending on the resistance ratio of outer and inner
tunnel junctions, one can realize either effective electron cooling in the
central N island or create highly nonequilibrium energy distributions of
electrons in both S and N islands. These distributions exhibit multiple peaks
at a distance of integer multiples of the superconducting chemical potential.
In the latter case the superconducting gap in the S islands is strongly
suppressed as compared to its equilibrium value
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
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
Parity-Affected Superconductivity in Ultrasmall Metallic Grains
We investigate the breakdown of BCS superconductivity in {\em ultra}\/small
metallic grains as a function of particle size (characterized by the mean
spacing between discrete electronic eigenstates), and the parity ( =
even/odd) of the number of electrons on the island. Assuming equally spaced
levels, we solve the parity-dependent BCS gap equation for the order parameter
. Both the critical level spacing and the
critical temperature at which are parity
dependent, and both are so much smaller in the odd than the even case that
these differences should be measurable in current experiments.Comment: 4 pages RevTeX, 1 encapsulated postscript figure, submitted to
Physical Review Letter
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