1,517 research outputs found
The structure functions of longitudinal virtual photon at low virtualities
The structure functions of longitudinal virtual photon at low virtualities
are calculated in the framework of chiral pertubation theory(ChPT) in the zero
and first order of ChPT. It is assumed that the virtuality of target
longitudinal photon is much less than the virtuality of the hard projectile
photon and both are less than the characteristic ChPT scale.Comment: 16 pages, 8 figure
Instantons in the Langevin dynamics: an application to spin glasses
We develop a general technique to calculate the probability of transitions
over the barriers in spin-glasses in the framework of the dynamical theory. We
use Lagrangian formulation of the instanton dynamics in which the transitions
are represented by instantons. We derive the full set of the equations that
determine the instantons but instead of solving them directly we prove that an
instanton process can be mapped into a usual process going back in time which
simplifies the problem significantly. We apply this general considerations to a
simple example of the spherical Sherrington-Kirkpatrick model and we find the
probability of the transition between the metastable states which is in
agreement with physical expectations.Comment: 18 pages, 2 figure
Performance analysis of an interacting quantum dot thermoelectric system
We analyze the nanocaloritronic performance of an interacting quantum dot
that is subject to an applied bias and an applied temperature gradient. It is
now well known that, in the absence of phonon contribution, a weakly coupled
non-interacting quantum dot can operate at thermoelectric efficiencies
approaching the Carnot limit. However, it has also been recently pointed out
that such peak efficiencies can only be achieved when operated in the
reversible limit, with a vanishing current and hence a vanishing power output.
In this paper, we point out three fundamental results affecting the
thermoelectric performance due to the inclusion of Coulomb interactions: a) The
reversible operating point carries zero efficiency, b) operation at finite
power output is possible even at peak efficiencies approaching the Carnot
value, and c) the evaluated trends of the the maximum efficiency deviate
considerably from the conventional {\it{figure of merit}} based result.
Finally, we also analyze our system for thermoelectric operation at maximum
power output.Comment: 10 pages, 6 figures, Resubmission- to be published in Phys. Rev.
New Two-Dimensional Integrable Quantum Models from SUSY Intertwining
Supersymmetrical intertwining relations of second order in the derivatives
are investigated for the case of supercharges with deformed hyperbolic metric
. Several classes of particular solutions of these
relations are found. The corresponding Hamiltonians do not allow the
conventional separation of variables, but they commute with symmetry operators
of fourth order in momenta. For some of these models the specific SUSY
procedure of separation of variables is applied.Comment: 18 page
Thermoelectric properties of Bi2Te3 atomic quintuple thin films
Motivated by recent experimental realizations of quintuple atomic layer films
of Bi2Te3,the thermoelectric figure of merit, ZT, of the quintuple layer is
calculated and found to increase by a factor of 10 (ZT = 7.2) compared to that
of the bulk at room temperature. The large enhancement in ZT results from the
change in the distribution of the valence band density of modes brought about
by the quantum confinement in the thin film. The theoretical model uses ab
initio electronic structure calculations (VASP) with full quantum-mechanical
structure relaxation combined with a Landauer formalism for the linear-response
transport coefficients.Comment: 4 figures, submitted to AP
Supersymmetrical Separation of Variables for Scarf II Model: Partial Solvability
Recently, a new quantum model - two-dimensional generalization of the Scarf
II - was completely solved analytically by SUSY method for the integer values
of parameter. Now, the same integrable model, but with arbitrary values of
parameter, will be studied by means of supersymmetrical intertwining relations.
The Hamiltonian does not allow the conventional separation of variables, but
the supercharge operator does allow, leading to the partial solvability of the
model. This approach, which can be called as the first variant of
SUSY-separation, together with shape invariance of the model, provides
analytical calculation of the part of spectrum and corresponding wave functions
(quasi-exact-solvability). The model is shown to obey two different variants of
shape invariance which can be combined effectively in construction of energy
levels and wave functions.Comment: 6 p.p., accepted for publication in EP
Transport properties in correlated systems: An analytical model
Several studies have so far investigated transport properties of strongly
correlated systems. Interesting features of these materials are the lack of
resistivity saturation well beyond the Mott-Ioffe-Regel limit and the scaling
of the resistivity with the hole density in underdoped cuprates. Due to the
strongly correlated nature of these materials, mainly numerical techniques have
been employed. A key role in this regards is thought to be played by the
continuous transfer of spectral weight from coherent to incoherent states. In
this paper we employ a simple analytical expression for the electronic Green's
function to evaluate both quasi-particle and transport properties in correlated
systems. Our analytical approach permits to enlighten the specific role of the
spectral transfer due to the correlation on different features. In particular
we investigate the dependence of both quasi-particle and transport scattering
rate on the correlation degree and the criterion for resistivity saturation.
systems.Comment: 11 pages, 8 figures. New version correcting a mistake of the previous
version and added figure
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