Persistent current noise and electron-electron interactions

We analyze fluctuations of persistent current (PC) produced by a charged quantum particle moving in a ring and interacting with a dissipative environment formed by diffusive electron gas. We demonstrate that in the presence of interactions such PC fluctuations persist down to zero temperature. In the case of weak interactions and/or sufficiently small values of the ring radius $R$ PC noise remains coherent and can be tuned by external magnetic flux $\Phi_x$ piercing the ring. In the opposite limit of strong interactions and/or large values of $R$ fluctuations in the electronic bath strongly suppress quantum coherence of the particle down to $T=0$ and induce incoherent $\Phi_x$-independent current noise in the ring which persists even at $\Phi_x=0$ when the average PC is absent.Comment: 12 pages, 8 figure

Practice of using the magnetic treatment devices to intensify the processes of primary oil treating

During the primary treatment of oil, gas and water, complications arise associated with the presence of hard water-oil emulsions, which cause an increase in fluid pressure in the gathering systems, pipeline damage, as well as difficulties in gas separation and preliminary water discharge at the preliminary discharge unit (PRU). Additional problems arise during transportation of highly paraffinic oils associated with the crystallization of paraffin in the flow path of the oilfield equipment and on the inner surface of pipes, leading to a drop in the productivity of pipelines.  Article discusses the technology of magnetic-reagent treatment of water-oil media, which allows intensifying the processes of primary oil treatment at the facilities of its production. Bench and pilot tests have shown the ability of the magnetic field to accelerate oil demulsification processes, increasing the percentage of separated water during subsequent settling, and to reduce asphalt-resin-paraffin deposits (ARPD) on the inner surface of oil and gas field equipment. Mechanism of the magnetic field effect on water-oil media is described. Effect of treatment on the integrity of the armour shells of oil-water emulsions was studied. Various modes of magnetic treatment have been investigated with evaluation of its effectiveness. It is shown that the best effect is achieved with the combined use of reagents and a magnetic field. Synergistic effect is observed, which consists in increasing their effectiveness. This made it possible to conclude that this method can be applied to reduce the consumption of reagents used in oil production while maintaining the treatment efficiency

Electron transport and current fluctuations in short coherent conductors

Employing a real time effective action formalism we analyze electron transport and current fluctuations in comparatively short coherent conductors in the presence of electron-electron interactions. We demonstrate that, while Coulomb interaction tends to suppress electron transport, it may {\it strongly enhance} shot noise in scatterers with highly transparent conducting channels. This effect of excess noise is governed by the Coulomb gap observed in the current-voltage characteristics of such scatterers. We also analyze the frequency dispersion of higher current cumulants and emphasize a direct relation between electron-electron interaction effects and current fluctuations in disordered mesoscopic conductors.Comment: 16 pages, 4 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

Parity effect and spontaneous currents in superconducting nanorings

New physical effects emerge from an interplay between the electron parity number and persistent currents in superconducting nanorings. An odd electron, being added to the ring, produces a countercurrent which may substantially modify the ground state properties of the system. In superconducting nanorings with an embedded normal metal layer a novel ``$\pi /N$-junction'' state can occur for the odd number of electrons. Changing this number from even to odd yields spontaneous supercurrent in the ground state of such rings without any externally applied magnetic flux. Further peculiar features of the parity effect are expected in structures with resonant electron transport across the weak link.Comment: 9 pages, 5 figures. Invited talk at the International Conference "Frontiers of Quantum and Mesoscopic Thermodynamics", Prague, July 200

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 $d$ between discrete electronic eigenstates), and the parity ($P$ = 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 $\Delta_P (d,T)$. Both the $T=0$ critical level spacing $d_{c,P}$ and the critical temperature $T_{c,P} (d)$ at which $\Delta_P = 0$ 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

Strong Charge Fluctuations in the Single-Electron Box: A Quantum Monte Carlo Analysis

We study strong electron tunneling in the single-electron box, a small metallic island coupled to an electrode by a tunnel junction, by means of quantum Monte Carlo simulations. We obtain results, at arbitrary tunneling strength, for the free energy of this system and the average charge on the island as a function of an external bias voltage. In much of the parameter range an extrapolation to the ground state is possible. Our results for the effective charging energy for strong tunneling are compared to earlier -- in part controversial -- theoretical predictions and Monte Carlo simulations

Zero-Point Fluctuations and the Quenching of the Persistent Current in Normal Metal Rings

The ground state of a phase-coherent mesoscopic system is sensitive to its environment. We investigate the persistent current of a ring with a quantum dot which is capacitively coupled to an external circuit with a dissipative impedance. At zero temperature, zero-point quantum fluctuations lead to a strong suppression of the persistent current with decreasing external impedance. We emphasize the role of displacement currents in the dynamical fluctuations of the persistent current and show that with decreasing external impedance the fluctuations exceed the average persistent current.Comment: 4 pages, 2 eps figure