Superconducting single-mode contact as a microwave-activated quantum interferometer

The dynamics of a superconducting quantum point contact biased at subgap voltages is shown to be strongly affected by a microwave electromagnetic field. Interference among a sequence of temporally localized, microwave-induced Landau-Zener transitions between current carrying Andreev levels results in energy absorption and in an increase of the subgap current by several orders of magnitude. The contact is an interferometer in the sense that the current is an oscillatory function of the inverse bias voltage. Possible applications to Andreev-level spectroscopy and microwave detection are discussed

Nanoelectromechanics of shuttle devices

A single-electron tunneling (SET) device with a nanoscale central island that can move with respect to the bulk source- and drain electrodes allows for a nanoelectromechanical (NEM) coupling between the electrical current through the device and mechanical vibrations of the island. Although an electromechanical "shuttle" instability and the associated phenomenon of single-electron shuttling were predicted more than 15 years ago, both theoretical and experimental studies of NEM-SET structures are still carried out. New functionalities based on quantum coherence, Coulomb correlations and coherent electron-spin dynamics are of particular current interest. In this article we present a short review of recent activities in this area.Comment: 23 pages, 26 figure

Coulomb Promotion of Spin-Dependent Tunnelling

We study transport of spin-polarized electrons through a magnetic single-electron transistor (SET) in the presence of an external magnetic field. Assuming the SET to have a nanometer size central island with a single electron level we find that the interplay on the island between coherent spin-flip dynamics and Coulomb interactions can make the Coulomb correlations promote rather than suppress the current through the device. We find the criteria for this new phenomenon -- Coulomb promotion of spin-dependent tunnelling -- to occur.Comment: 4 pages, 3 figures; The new version has a slightly modified title, 2 more figures, and an extended analysis of the (same) results obtaine

Electrical Manipulation of Nanomagnets

We demonstrate a possibility to manipulate the magnetic coupling between two nanomagnets with a help of ac electric field. In the scheme suggested the magnetic coupling in question is mediated by a magnetic particle contacting with both of the nanomagnets through the tunnel barriers. The electric field providing a successive suppression of the barriers leads to pumping of magnetization through the mediating particle. Time dependent dynamics of the particle magnetization allows to to switch between ferro- and antiferromagnetic couplings.Comment: 4 pages, 2 figure

High-temperature excess current and quantum suppression of electronic backscattering in a 1-D system

We consider the electronic current through a one-dimensional conductor in the ballistic transport regime and show that the quantum oscillations of a weakly pinned single scattering target results in a temperature- and bias-voltage independent excess current at large bias voltages. This is a genuine effect on transport that derives from an exponential reduction of electronic backscattering in the elastic channel due to quantum delocalization of the scatterer and from suppression of low-energy electron backscattering in the inelastic channels caused by the Pauli exclusion principle. We show that both the mass of the target and the frequency of its quantum vibrations can be measured by studying the differential conductance and the excess current. We apply our analysis to the particular case of a weakly pinned C60 molecule encapsulated by a single-wall carbon nanotube and find that the discussed phenomena are experimentally observable.Comment: 4 pages, 4 figure