Kvantno-elektrodinamičke pospravke za polarizirano Møllerovo raspršenje

Principal contributions to QED radiative effects for Moller scattering of polarized particles are investigated. Explicit formulae for the cross section of radiative effects are given in covariant form. A FORTRAN code based on exact expressions for radiative corrections to cross section was used to calculate the results. Detailed numerical analysis for cross sections as well as for polarization asymmetries is given.Istražuju se glavni doprinosi kvantno-elektrodinamičkih popravaka za Møllerovo raspršenje polariziranih čestica. Izlažu se podrobni ishodi računa za udarne presjeke i polarizacijske asimetrije

Kvantno-elektrodinamičke pospravke za polarizirano Møllerovo raspršenje

Principal contributions to QED radiative effects for Moller scattering of polarized particles are investigated. Explicit formulae for the cross section of radiative effects are given in covariant form. A FORTRAN code based on exact expressions for radiative corrections to cross section was used to calculate the results. Detailed numerical analysis for cross sections as well as for polarization asymmetries is given.Istražuju se glavni doprinosi kvantno-elektrodinamičkih popravaka za Møllerovo raspršenje polariziranih čestica. Izlažu se podrobni ishodi računa za udarne presjeke i polarizacijske asimetrije

Dissipative charge transport in diffusive superconducting double-barrier junctions

We solve the coherent multiple Andreev reflection (MAR) problem and calculate current-voltage characteristics (IVCs) for Josephson SINIS junctions, where S are local-equilibrium superconducting reservoirs, I denotes tunnel barriers, and N is a short diffusive normal wire, the length of which is much smaller than the coherence length, and the resistance is much smaller than the resistance of the tunnel barriers. The charge transport regime in such junctions qualitatively depends on a characteristic value \gamma = \Delta \tau_d of relative phase shifts between the electrons and retro-reflected holes accumulated during the dwell time \tau_d. In the limit of small electron-hole dephasing \gamma << 1, our solution recovers a known formula for a short mesoscopic connector extended to the MAR regime. At large dephasing, the subharmonic gap structure in the IVC scales with 1/ \gamma, which thus plays the role of an effective tunneling parameter. In this limit, the even gap subharmonics are resonantly enhanced, and the IVC exhibits portions with negative differential resistance.Comment: 8 pages, 3 figures, typos corrected, to be published in Phys. Rev.

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

Subgap current in superconducting tunnel junctions with diffusive electrodes

We calculate the subgap current in planar superconducting tunnel junctions with thin-film diffusive leads. It is found that the subharmonic gap structure of the tunnel current scales with an effective tunneling transparency which may exceed the junction transparency by up to two orders of magnitude depending on the junction geometry and the ratio between the coherence length and the elastic scattering length. These results provide an alternative explanation of anomalously high values of the subgap current in tunnelling experiments often ascribed to imperfection of the insulating layer. We also discuss the effect of finite lifetime of quasiparticles as the possible origin of additional enhancement of multiparticle tunnel currents.Comment: 4 pages, 4 figures, to be published in Phys. Rev.