Single-level resonance parameters fit nuclear cross-sections

Least squares analyses of experimental differential cross-section data for the U-235 nucleus have yielded single level Breit-Wigner resonance parameters that fit, simultaneously, three nuclear cross sections of capture, fission, and total

Transport through single-level systems: Spin dynamics in the nonadiabatic regime

We investigate the Fano-Anderson model coupled to a large ensemble of spins under the influence of an external magnetic field. The interaction between the two spin systems is treated within a meanfield-approach and we assume an anisotropic coupling between these two systems. By using a nonadiabatic approach, we make no further approximations in the theoretical description of our system, apart from the semiclassical treatment. Therewith, we can include the short-time dynamics as well as the broadening of the energy levels arising due to the coupling to the external electronic reservoirs. We study the spin dynamics in the regime of low and high bias. For the infinite bias case, we compare our results to those obtained from a simpler rate equation approach, where higher-order transitions are neglected. We show, that these higher-order terms are important in the range of low magnetic field. Additionally, we analyze extensively the finite bias regime with methods from nonlinear dynamics, and we discuss the possibility of switching of the large spin.Comment: 16 pages, 16 figure

Spin-polarized transport through a single-level quantum dot in the Kondo regime

Nonequilibrium electronic transport through a quantum dot coupled to ferromagnetic leads (electrodes) is studied theoretically by the nonequilibrium Green function technique. The system is described by the Anderson model with arbitrary correlation parameter $U$. Exchange interaction between the dot and ferromagnetic electrodes is taken into account {\it via} an effective molecular field. The following situations are analyzed numerically: (i) the dot is symmetrically coupled to two ferromagnetic leads, (ii) one of the two ferromagnetic leads is half-metallic with almost total spin polarization of electron states at the Fermi level, and (iii) one of the two electrodes is nonmagnetic whereas the other one is ferromagnetic. Generally, the Kondo peak in the density of states (DOS) becomes spin-split when the total exchange field acting on the dot is nonzero. The spin-splitting of the Kondo peak in DOS leads to splitting and suppression of the corresponding zero bias anomaly in the differential conductance.Comment: 9 pages, 7 figure

Universal single level implicit algorithm for gasdynamics

A single level effectively explicit implicit algorithm for gasdynamics is presented. The method meets all the requirements for unconditionally stable global iteration over flows with mixed supersonic and supersonic zones including blunt body flow and boundary layer flows with strong interaction and streamwise separation. For hyperbolic (supersonic flow) regions the method is automatically equivalent to contemporary space marching methods. For elliptic (subsonic flow) regions, rapid convergence is facilitated by alternating direction solution sweeps which bring both sets of eigenvectors and the influence of both boundaries of a coordinate line equally into play. Point by point updating of the data with local iteration on the solution procedure at each spatial step as the sweeps progress not only renders the method single level in storage but, also, improves nonlinear accuracy to accelerate convergence by an order of magnitude over related two level linearized implicit methods. The method derives robust stability from the combination of an eigenvector split upwind difference method (CSCM) with diagonally dominant ADI(DDADI) approximate factorization and computed characteristic boundary approximations

Resonant polaron-assisted tunneling of strongly interacting electrons through a single-level vibrating quantum dot

The problem of resonant transport of strongly interacting electrons through a one-dimensional single-level vibrating quantum dot is being considered. In this paper, we generalize the Komnik and Gogolin model [Phys. Rev. Lett., 90, 246403, (2003)] for the single-electron transistor with g=1/2 Luttinger liquid leads to the case of a strong electron-vibron interaction in a quantum dot. The effective transmission coefficient and differential conductance of the system has been derived for the general case of asymmetric tunnel barriers. The main result obtained is that, in the zero-temperature limit, the resonant polaron-assisted tunneling with perfect transmission is possible. This resonant tunneling is of the novel (Andreev-like) type due to a special electron-electron interaction in the leads. As a result, a strong domination of resonant polaron-assisted electron transport at low temperatures has been found. Additional narrowing due to electron-electron interaction in the leads, is roughly the same for all polaron-assisted resonances.Comment: 9 pages, 3 figure

Theory of Current and Shot Noise Spectroscopy in Single-Molecular Quantum Dots with Phonon Mode

Using the Keldysh nonequilibrium Green function technique, we study the current and shot noise spectroscopy of a single molecular quantum dot coupled to a local phonon mode. It is found that in the presence of electron-phonon coupling, in addition to the resonant peak associated with the single level of the dot, satellite peaks with the separation set by the frequency of phonon mode appear in the differential conductance. In the ``single level'' resonant tunneling region, the differential shot noise power exhibit two split peaks. However, only single peaks show up in the ``phonon assisted'' resonant-tunneling region. An experimental setup to test these predictions is also proposed.Comment: 5 pages, 3 eps figures embedde