Mesoscopic charge quantization

We study the Coulomb blockade in a chaotic quantum dot connected to a lead by a single channel at nearly perfect transmission. We take into account quantum fluctuations of the dot charge and a finite level spacing for electron states within the dot. Mesoscopic fluctuations of thermodynamic and transport properties in the Coulomb blockade regime exist at any transmission coefficient. In contrast to the previous theories, we show that by virtue of these mesoscopic fluctuations, the Coulomb blockade is not destroyed completely even at perfect transmission. The oscillatory dependence of all the observable characteristics on the gate voltage is preserved, its period is still defined by the charge of a single electron. However, phases of those oscillations are random; because of the randomness, the Coulomb blockade shows up not in the averages but in the correlation functions of the fluctuating observables (e.g., capacitance or tunneling conductance). This phenomenon may be called "mesoscopic charge quantization".Comment: 34 two-column pages, latex, 9 .eps figures include

Divergence of the Classical trajectories and Weak Localization

We study the weak localization correction (WLC) to transport coefficients of a system of electrons in a static long-range potential (e.g. an antidot array or ballistic cavity). We found that the weak localization correction to the current response is delayed by the large time $t_E = \lambda^{-1} |\ln \hbar|$, where $\lambda$ is the Lyapunov exponent. In the semiclassical regime $t_E$ is much larger than the transport lifetime. Thus, the fundamental characteristic of the classical chaotic motion, Lyapunov exponent, may be found by measuring the frequency or temperature dependence of WLC.Comment: 23 pages, 4 .eps figures; Major revisions in Secs. 3, 4, and 6; To appear in Phys. Rev. B, Nov. 15, 199

Effects of electron-electron interaction on the conductance of open quantum dots

We study the effect of electron-electron interaction on the conductance of open quantum dots. We find that Coulomb interactions (i) do not affect the ensemble averaged conductance if time-reversal symmetry has been broken by a magnetic field, (ii) enhance weak localization and weak anti-localization corrections to in the absence of a magnetic field, (iii) increase conductance fluctuations, and (iv) enhance the effect of short trajectories on the conductivity of quantum dot.Comment: 4 pages, RevTeX; 1 figure include

Mesoscopic fluctuations of the Coulomb drag

We consider mesoscopic fluctuations of the Coulomb drag coefficient $\rho_D$ in the system of two separated two-dimensional electron gases. It is shown that at low temperatures sample to sample fluctuations of $\rho_D$ exceed its ensemble average. It means that in such a regime the sign of $\rho_D$ is random and the temperature dependence almost saturates $\rho_D \sim 1/\sqrt{T}$.Comment: 4 pages, 4 eps figure

Shifts of Random Energy Levels by a Local Perturbation

We consider the effect of a local perturbation on the energy levels of a system described by random matrix theory. An analytic expression for the joint distribution function of initial and final energy levels is obtained. In the case of unitary ensemble we also find the two-point correlation function of initial and final densities of states.Comment: 4 page

Phase Fluctuations and Non-Equilibrium Josephson Effect

We consider a diffusive S-N-S junction with electrons in the normal layer driven out of equilibrium by external bias. We show that, the non-equilibrium fluctuations of the electron density in the normal layer cause the fluctuations of the phase of the order parameter in the S-layers. As a result, the magnitude of the Josephson current in the non-equilibrium junction is significantly supressed relative to its mean field value.Comment: 4 pages, 1 .eps figure; References adde

Supersymmetric low-energy theory and renormalization group for a clean Fermi gas with a repulsion in arbitrary dimensions

We suggest a new method of calculations for a clean Fermi gas with a repulsion in any dimension. This method is based on writing equations for quasiclassical Green functions and reducing them to equations for collective spin and charge excitations. The spin excitations interact with each other and this leads to non-trivial physics. Writing the solution of the equations and the partition function in terms of a functional integral over supervectors and averaging over fluctuating fields we come to an effective field theory describing the spin excitations. In some respects, the theory is similar to bosonization but also includes the ``ghost'' excitations which prevents overcounting of the degrees of freedom. Expansion in the interaction reveals logarithmic in temperature corrections. This enables us to suggest a renormalization group scheme and derive renormalization group equations. Solving these equations and using their solutions for calculating thermodynamic quantities we obtain explicit expression for the specific heat containing only an effective amplitude of the backward scattering. This amplitude has a complicated dependence on the logarithm of temperature, which leads to a non-trivial temperature dependence of the specific heat

The internal structure of a vortex in a two-dimensional superfluid with long healing length and its implications

We analyze the motion of quantum vortices in a two-dimensional spinless superfluid within Popov's hydrodynamic description. In the long healing length limit (where a large number of particles are inside the vortex core) the superfluid dynamics is determined by saddle points of Popov's action, which, in particular, allows for weak solutions of the Gross-Pitaevskii equation. We solve the resulting equations of motion for a vortex moving with respect to the superfluid and find the reconstruction of the vortex core to be a non-analytic function of the force applied on the vortex. This response produces an anomalously large dipole moment of the vortex and, as a result, the spectrum associated with the vortex motion exhibits narrow resonances lying {\em within} the phonon part of the spectrum, contrary to traditional view.Comment: 45 pages, 8 figure

Theory of Dephasing by External Perturbation in Open Quantum Dots

We propose a random matrix theory describing the influence of a time dependent external field on the average magnetoresistance of open quantum dots. The effect is taken into account in all orders of perturbation theory, and the result is applicable to both weak and strong external fields.Comment: 4 pages, 3 figure

Phonon effects in molecular transistors

A rate equation formalism is used to determine the effect of electron-phonon coupling on the conductance of a molecule. Interplay between the phonon-induced renormalization of the density of states on the quantum dot and the phonon-induced renormalization of the dot-lead coupling is found to be important. Whether or not the phonons are able to equilibrate in a time rapid compared to the transit time of an electron through the dot is found to affect the conductance. Observable signatures of phonon equilibration are presented.Comment: 4 pages, 4 figure