1,486 research outputs found

### Microwave Response of V3Si Single Crystals: Evidence for Two-Gap Superconductivity

The investigation of the temperature dependences of microwave surface
impedance and complex conductivity of V3Si single crystals with different
stoichiometry allowed to observe a number of peculiarities which are in
remarkable contradiction with single-gap Bardeen-Cooper-Schrieffer theory. At
the same time, they can be well described by two-band model of
superconductivity, thus strongly evidencing the existence of two distinct
energy gaps with zero-temperature values Delta1~1.8Tc and Delta2~0.95Tc in
V3Si.Comment: Submitted to Europhysics Letter

### Light-induced valley currents and magnetization in graphene rings

We study the non-equilibrium dynamics in a mesoscopic graphene ring excited
by picoseconds shaped electromagnetic pulses. We predict an ultrafast buildup
of charge polarization, currents and orbital magnetization. Applying the light
pulses identified here, non-equilibrium valley currents are generated in a
graphene ring threaded by a stationary magnetic flux. We predict a finite
graphene ring magnetization even for a vanishing charge current; the
magnetization emerges due to the light-induced difference of the valley
populations.Comment: 4 pages, 2 figures, submitted to Phys. Rev.

### Interaction of strongly correlated electrons and acoustical phonons

We investigate the interaction of correlated electrons with acoustical
phonons using the extended Hubbard-Holstein model in which both, the
electron-phonon interaction and the on-site Coulomb repulsion are considered to
be strong. The Lang-Firsov canonical transformation allows to obtain mobile
polarons for which a new diagram technique and generalized Wick's theorem is
used. This allows to handle the Coulomb repulsion between the electrons emerged
into a sea of phonon fields (\textit{phonon clouds}). The physics of emission
and absorption of the collective phonon-field mode by the polarons is discussed
in detail. Moreover, we have investigated the different behavior of optical and
acoustical phonon clouds when propagating through the lattice. In the
strong-coupling limit of the electron-phonon interaction, and in the normal as
well as in the superconducting phase, chronological thermodynamical averages of
products of acoustical phonon-cloud operators can be expressed by one-cloud
operator averages. While the normal one-cloud propagator has the form of a
Lorentzian, the anomalous one is of Gaussian form and considerably smaller.
Therefore, the anomalous electron Green's functions can be considered to be
more important than corresponding polarons functions, i.e., pairing of
electrons without phonon-clouds is easier to achieve than pairing of polarons
with such clouds.Comment: : 28 pages, 9 figures, revtex4. Invited paper for a special issue of
Low Temperature Physics dedicated to the 20th anniversary of HTS

### Radiative damping and synchronization in a graphene-based terahertz emitter

We investigate the collective electron dynamics in a recently proposed
graphene-based terahertz emitter under the influence of the radiative damping
effect, which is included self-consistently in a molecular dynamics approach.
We show that under appropriate conditions synchronization of the dynamics of
single electrons takes place, leading to a rise of the oscillating component of
the charge current. The synchronization time depends dramatically on the
applied dc electric field and electron scattering rate, and is roughly
inversely proportional to the radiative damping rate that is determined by the
carrier concentration and the geometrical parameters of the device. The
emission spectra in the synchronized state, determined by the oscillating
current component, are analyzed. The effective generation of higher harmonics
for large values of the radiative damping strength is demonstrated.Comment: 9 pages, 7 figure

### Detecting Bose-Einstein condensation of exciton-polaritons via electron transport

We examine the Bose-Einstein condensation of exciton-polaritons in a
semiconductor microcavity via an electrical current. We propose that by
embedding a quantum dot p-i-n junction inside the cavity, the tunneling current
through the device can reveal features of condensation due to a one-to-one
correspondence of the photons to the condensate polaritons. Such a device can
also be used to observe the phase interference of the order parameters from two
condensates.Comment: 5 Pages, 3 Figure

### Diagrammatic theory for Periodic Anderson Model: Stationary property of the thermodynamic potential

Diagrammatic theory for Periodic Anderson Model has been developed, supposing
the Coulomb repulsion of $f-$ localized electrons as a main parameter of the
theory. $f-$ electrons are strongly correlated and $c-$ conduction electrons
are uncorrelated. Correlation function for $f-$ and mass operator for $c-$
electrons are determined. The Dyson equation for $c-$ and Dyson-type equation
for $f-$ electrons are formulated for their propagators. The skeleton diagrams
are defined for correlation function and thermodynamic functional. The
stationary property of renormalized thermodynamic potential about the variation
of the mass operator is established. The result is appropriate as for normal
and as for superconducting state of the system.Comment: 12 pages, 10 figure

### Propagation of cosmic rays: nuclear physics in cosmic-ray studies

The nuclei fraction in cosmic rays (CR) far exceeds the fraction of other CR
species, such as antiprotons, electrons, and positrons. Thus the majority of
information obtained from CR studies is based on interpretation of isotopic
abundances using CR propagation models where the nuclear data and isotopic
production cross sections in p- and alpha-induced reactions are the key
elements. This paper presents an introduction to the astrophysics of CR and
diffuse gamma rays and discusses some of the puzzles that have emerged recently
due to more precise data and improved propagation models. Merging with
cosmology and particle physics, astrophysics of CR has become a very dynamic
field with a large potential of breakthrough and discoveries in the near
future. Exploiting the data collected by the CR experiments to the fullest
requires accurate nuclear cross sections.Comment: 6 pages, 13 figures, aip style files. Invited review talk at the Int.
Conf. on Nuclear Data-2004 (Santa Fe, Sep. 26 - Oct. 1, 2004). To appear in
AIP Conf. Pro

- …