Nonlinear transport through a dynamic impurity in a strongly interacting one-dimensional electron gas

We analyze the transport properties of a Luttinger liquid with an imbedded impurity of explicitly time-dependent strength. We employ a radiative boundary condition formalism to describe the coupling to the voltage sources. Assuming the impurity time dependence to be oscillatory we present a full analytic perturbative result in impurity strength for arbitrary interaction parameter calculated with help of Coulomb gas expansion (CGE). Moreover, a full analytic solution beyond the above restriction is possible for a special non-trivial interaction strength which has been achieved independently by full resummation of CGE series as well as via refermionization technique. The resulting nonlinear current-voltage characteristic turns out to be very rich due to the presence of the additional energy scale associated with the impurity oscillation frequency. In accordance with the previous studies we also find an enhancement of the linear conductance of the wire to values above the unitary limit G0 = 2e2/h.Comment: 8 pages, 3 figures, submitted to PR

Transient dynamics of a molecular quantum dot with a vibrational degree of freedom

We investigate the transient effects occurring in a molecular quantum dot described by an Anderson-Holstein Hamiltonian which is instantly coupled to two fermionic leads biased by a finite voltage. In the limit of weak electron-phonon interaction, we use perturbation theory to determine the time-dependence of the dot population and the average current. The limit of strong coupling is accessed by means of a self-consistent time-dependent mean-field approximation. These comple- mentary approaches allow us to investigate the dynamics of the inelastic effects occurring when the applied bias voltage exceeds the phonon frequency and the emergence of bistability.Comment: 7 pages, 4 figure

Automatic design of optical systems by digital computer

Computer program uses geometrical optical techniques and a least squares optimization method employing computing equipment for the automatic design of optical systems. It evaluates changes in various optical parameters, provides comprehensive ray-tracing, and generally determines the acceptability of the optical system characteristics

Charge transfer statistics of a molecular quantum dot with strong electron-phonon interaction

We analyze the nonequilibrium transport properties of a quantum dot with a harmonic degree of freedom (Holstein phonon) coupled to metallic leads, and derive its full counting statistics (FCS). Using the Lang-Firsov (polaron) transformation, we construct a diagrammatic scheme to calculate the cumulant generating function. The electron-phonon interaction is taken into account exactly, and the employed approximation represents a summation of a diagram subset with respect to the tunneling amplitude. By comparison to Monte Carlo data the formalism is shown to capture the basic properties of the strong coupling regime

Full counting statistics of spin transfer through ultrasmall quantum dots

We analyze the spin-resolved full counting statistics of electron transfer through an ultrasmall quantum dot coupled to metallic electrodes. Modelling the setup by the Anderson Hamiltonian, we explicitly take into account the onsite Coulomb repulsion $U$. We calculate the cumulant generating function for the probability to transfer a certain number of electrons with a preselected spin orientation during a fixed time interval. With the cumulant generating function at hand we are then able to calculate the spin current correlations which are of outmost importance in the emerging field of spintronics. We confirm the existing results for the charge statistics and report the discovery of the new type of correlation between the spin-up and -down polarized electrons flows, which has a potential to become a powerful new instrument for the investigation of the Kondo effect in nanostructures.Comment: 5 pages, 1 figur

No new limit on the size distribution of gamma-ray bursts

The results of a study (Carter et. al.) of gamma ray bursts using long duration balloon exposure are analyzed. Arguments are presented against the conclusion that the size spectrum extrapolates to a power law with index from -1.0 to -0.5, and that therefore the gamma ray bursts are of galactic origin. It is claimed that the data are consistent with an upper limit over 100 times that proposed, and that therefore no conclusion can be drawn from the measurements regarding the nature or origin of gamma ray bursts. The resulting upper limit to the rate of occurrence of small bursts lies above the -1.5 index power law extrapolation of the size spectrum of known events, i.e., greater than the rate expected from an infinitely extended source region

Spin Effects in the Local Density of States of GaAs

We present spin-resolved measurements of the local density of states in Si doped GaAs. Both spin components exhibit strong mesoscopic fluctuations. In the magnetic quantum limit, the main features of the spin-up and spin-down components of the local density of states are found to be identical apart from Zeeman splitting. Based on this observation, we introduce a mesoscopic method to measure the $g$-factor in a material where macroscopic methods are severely restricted by disorder. Differences between the spin-up and spin-down components are discussed in terms of spin relaxation due to spin-orbit coupling.Comment: 4 pages and 5 figure

Understanding co-operative R&D activity: evidence from four European countries

This paper investigates co-operative research activity by firms using data from the 3rd Community Innovation Survey for four countries, France, Germany, Spain and the UK. We build on the Cassiman and Veugelers (CV) (2002) study of Belgian manufacturing firms, by incorporating information on the service sector, and considering the role of public support in affecting firms’ decisions to co-operate. Our results support those in CV, in that we find a positive relationship between the likelihood of undertaking co-operative R&D and both incoming knowledge spillovers and the extent to which firms find strategic methods important in appropriating the returns to innovative activity. We find that public support is positively related to the probability of undertaking co-operative agreements particularly with regard to the likelihood of co-operation with the research base. We find some evidence, in particular for Spain, that firms carry out co-operative R&D to overcome excessive perceived risks and financial constraints

Fano interference effect on the transition spectrum of single electron transistors

We theoretically study the intraband transition spectrum of single electron transistors (SETs) composed of individual self-assembled quantum dots. The polarization of SETs is obtained by using the nonequilibrium Green's function technique and the Anderson model with three energy levels. Owing to nonradiative coupling between two excited states through the continuum of electrodes, the Fano interference effect significantly influences the peak position and intensity of infrared wavelength single-photon spectrum.Comment: 4 pages, 5 figure