4,729 research outputs found
Spin-Hall Conductivity in Electron-Phonon Coupled Systems
We derive the ac spin-Hall conductivity of
two-dimensional spin-orbit coupled systems interacting with dispersionless
phonons of frequency . For the linear Rashba model we show that the
electron-phonon contribution to the spin-vertex corrections breaks the
universality of at low-frequencies and provides a
non-trivial renormalization of the interband resonance. On the contrary, in a
generalized Rashba model for which the spin-vertex contributions are absent,
the coupling to the phonons enters only through the self-energy, leaving the
low frequency behavior of unaffected by the
electron-phonon interaction.Comment: 4 pages, 3 figures, version as printe
Electron-phonon effects on spin-orbit split bands of two dimensional systems
The electronic self-energy is studied for a two dimensional electron gas
coupled to a spin-orbit Rashba field and interacting with dispersionless
phonons. For the case of a momentum independent electron-phonon coupling
(Holstein model) we solve numerically the self-consistent non-crossing
approximation for the self-energy and calculate the electron mass enhancement
and the spectral properties. We find that, even for nominal weak
electron-phonon interaction, for strong spin-orbit couplings the electrons
behave as effectively strongly coupled to the phonons. We interpret this result
by a topological change of the Fermi surface occurring at sufficiently strong
spin-orbit coupling, which induces a square-root divergence in the electronic
density of states at low energies. We provide results for and for the
density of states of the interacting electrons for several values of the
electron filling and of the spin-orbit interaction.Comment: 9 pages, 6 figures. Version as printe
Evidence of a new low field cross-over in the vortex critical velocity of type-II superconducting thin films
We measure current-voltage characteristics as function of magnetic field and
temperature in Nb strips of different thickness and width. The instability
voltage of the flux flow state related to the vortex critical velocity v* is
studied and compared with the Larkin-Ovchinnikov theory. Beside the usual
power-law dependence v* ~ B^-1/2, in the low field range a new cross-over
field, Bcr1, is observed below which v* decreases by further lowering the
external magnetic field B. We ascribe this unexpected cross-over to vortex
channeling due to a fan-like penetration of the applied magnetic field as
confirmed by magneto-optic imaging. The observation of Bcr1 becomes a direct
evidence of a general feature in type-II superconducting films at low fields,
that is a channel-like vortex motion induced by the inhomogeneous magnetic
state caused by the relatively strong pinning
Pauli susceptibility of nonadiabatic Fermi liquids
The nonadiabatic regime of the electron-phonon interaction leads to behaviors
of some physical measurable quantities qualitatively different from those
expected from the Migdal-Eliashberg theory. Here we identify in the Pauli
paramagnetic susceptibility one of such quantities and show that the
nonadiabatic corrections reduce with respect to its adiabatic limit. We
show also that the nonadiabatic regime induces an isotope dependence of ,
which in principle could be measured.Comment: 7 pages, 3 figures, euromacr.tex, europhys.sty. Replaced with
accepted version (Europhysics Letters
Per un pugno di opere
La svolta decisa dal governo per le infrastrutture medie e piccole dovrebbe essere adottata anche per quelle grandi, abbandonando così
l’idea che le opere “strategiche” generino una forte domanda. Altrimenti, dovremo rassegnarci ai cantieri “stop and go”. E al moltiplicarsi dei
costi
Multivariate linear parametric models applied to daily rainfall time series
International audienceThe aim of this paper is to test the Multivariate Linear Parametric Models applied to daily rainfall series. These simple models allow to generate synthetic series preserving both the time correlation (autocorrelation) and the space correlation (crosscorrelation). To have synthetic daily series, in such a way realistic and usable, it is necessary the application of a corrective procedure, removing negative values and enforcing the no-rain probability. The following study compares some linear models each other and points out the roles of autoregressive (AR) and moving average (MA) components as well as parameter orders and mixed parameters
Tav e grandi opere: non è solo un problema di costi
Le grandi opere non solo costano tanto, ma sono spesso inutili. Per giustificarle ci si affida a previsioni di aumento del traffico poco
realistiche. Sono necessarie analisi costi-benefici terze, indipendenti e interamente riproducibili
Topological Change of the Fermi Surface in Low Density Rashba Gases: Application to Superconductivity
Strong spin-orbit coupling can have a profound effect on the electronic
structure in a metal or semiconductor, particularly for low electron
concentrations. We show how, for small values of the Fermi energy compared to
the spin-orbit splitting of Rashba type, a topological change of the Fermi
surface leads to an effective reduction of the dimensionality in the electronic
density of states. We investigate its consequences on the onset of the
superconducting instability. We show, by solving the Eliashberg equations for
the critical temperature as a function of spin-orbit coupling and electron
density, that the superconducting critical temperature is significantly tuned
in this regime by the spin-orbit coupling. We suggest that materials with
strong spin-orbit coupling are good candidates for enhanced superconductivity.Comment: 5 pages, 2 figures ep
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