Weak localization in a system with a barrier: Dephasing and weak Coulomb blockade

We non-perturbatively analyze the effect of electron-electron interactions on weak localization (WL) in relatively short metallic conductors with a tunnel barrier. We demonstrate that the main effect of interactions is electron dephasing which persists down to T=0 and yields suppression of WL correction to conductance below its non-interacting value. Our results may account for recent observations of low temperature saturation of the electron decoherence time in quantum dots.Comment: published version, 10 page

Strong Tunneling and Coulomb Blockade in a Single-Electron Transistor

We have developed a detailed experimental study of a single-electron transistor in a strong tunneling regime. Although weakened by strong charge fluctuations, Coulomb effects were found to persist in all samples including one with the effective conductance 8 times higher than the quantum value (6.45 k$\Omega$)$^{-1}$. A good agreement between our experimental data and theoretical results for the strong tunneling limit is found. A reliable operation of transistors with conductances 3-4 times larger than the quantum value is demonstrated.Comment: revtex, 4 page

Strong Electron Tunneling through a Small Metallic Grain

Electron tunneling through mesoscopic metallic grains can be treated perturbatively only provided the tunnel junction conductances are sufficiently small. If it is not the case, fluctuations of the grain charge become strong. As a result (i) contributions of all -- including high energy -- charge states become important and (ii) excited charge states become broadened and essentially overlap. At the same time the grain charge remains discrete and the system conductance $e$-periodically depends on the gate charge. We develop a nonperturbative approach which accounts for all these features and calculate the temperature dependent conductance of the system in the strong tunneling regime at different values of the gate charge.Comment: revtex, 8 pages, 2 .ps figure

Persistent current noise

We demonstrate that persistent current in meso- and nanorings may fluctuate down to zero temperature provided the current operator does not commute with the total Hamiltonian of the system. For a model of a quantum particle on a ring we explicitly evaluate PC noise power which has a form of sharp peaks which become broadened for multi-channel rings or in the presence of dissipation. PC noise can be tuned by an external magnetic flux which is a fundamental manifestation of quantum coherence in the system.Comment: 4 pages, 1 figur

Coulomb blockade of non-local electron transport in metallic conductors

We consider a metallic wire coupled to two metallic electrodes via two junctions placed nearby. A bias voltage applied to one of such junctions alters the electron distribution function in the wire in the vicinity of another junction thus modifying both its noise and the Coulomb blockade correction to its conductance. We evaluate such interaction corrections to both local and non-local conductances demonstrating non-trivial Coulomb anomalies in the system under consideration. Experiments on non-local electron transport with Coulomb effects can be conveniently used to test inelastic electron relaxation in metallic conductors at low temperatures.Comment: Published version. 11 pages, 4 figures. New references added, discussion and introduction are extended, appendices adde

Penalized maximum likelihood and semiparametric second-order efficiency

We consider the problem of estimation of a shift parameter of an unknown symmetric function in Gaussian white noise. We introduce a notion of semiparametric second-order efficiency and propose estimators that are semiparametrically efficient and second-order efficient in our model. These estimators are of a penalized maximum likelihood type with an appropriately chosen penalty. We argue that second-order efficiency is crucial in semiparametric problems since only the second-order terms in asymptotic expansion for the risk account for the behavior of the ``nonparametric component'' of a semiparametric procedure, and they are not dramatically smaller than the first-order terms.Comment: Published at http://dx.doi.org/10.1214/009053605000000895 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Magnetoresistance of n-GaAs at filamentary current flow

A large number of sharp structures are observed in the 4.2 K magnetoresistance of n-GaAs biased above impurity breakdown in a regime where current flow is filamentary. Most of the structures cannot be attributed to spectral properties of the semiconductor such as impact excitation of shallow donors or the magnetoimpurity effect. Experimental results give evidence that these structures are caused by a redistribution of the filamentary current flow when one filament border is swept across an imperfection in the material

Coulomb blockade in one-dimensional arrays of high conductance tunnel junctions

Properties of one-dimensional (1D) arrays of low Ohmic tunnel junctions (i.e. junctions with resistances comparable to, or less than, the quantum resistance $R_{\rm q}\equiv h/e^2\approx 25.8$ k$\Omega$) have been studied experimentally and theoretically. Our experimental data demonstrate that -- in agreement with previous results on single- and double-junction systems -- Coulomb blockade effects survive even in the strong tunneling regime and are still clearly visible for junction resistances as low as 1 k$\Omega$. We have developed a quasiclassical theory of electron transport in junction arrays in the strong tunneling regime. Good agreement between the predictions of this theory and the experimental data has been observed. We also show that, due to both heating effects and a relatively large correction to the linear relation between the half-width of the conductance dip around zero bias voltage, $V_{1/2}$, and the measured electronic temperature, such arrays are inferior to those conventionally used in the Coulomb Blockade Thermometry (CBT). Still, the desired correction to the half-width, $\Delta V_{1/2}$, can be determined rather easily and it is proportional to the magnitude of the conductance dip around zero bias voltage, $\Delta G$. The constant of proportionality is a function of the ratio of the junction and quantum resistances, $R/R_{\rm q}$, and it is a pure strong tunneling effect.Comment: LaTeX file + five postscript figure

Coulomb Interaction and Quantum Transport through a Coherent Scatterer

An interplay between charge discreteness, coherent scattering and Coulomb interaction yields nontrivial effects in quantum transport. We derive a real time effective action and an equivalent quantum Langevin equation for an arbitrary coherent scatterer and evaluate its current-voltage characteristics in the presence of interactions. Within our model, at large conductances $G_0$ and low $T$ (but outside the instanton-dominated regime) the interaction correction to $G_0$ saturates and causes conductance suppression by a universal factor which depends only on the type of the conductor.Comment: 4 pages, no figure