6,177 research outputs found
Using datasets from the Internet for hydrological modeling: an example from the Kntnk Menderes Basin, Turkey
River basin development / Water resources / Data collection / Models / Hydrology / Land classification / Water management / Water scarcity / Water allocation / Stream flow / Water demand / Turkey / Kntnk Menderes Basin
Graphene in periodically alternating magnetic field: unusual quantization of the anomalous Hall effect
We study the energy spectrum and electronic properties of graphene in a
periodic magnetic field of zero average with a symmetry of triangular lattice.
The periodic field leads to formation of a set of minibands separated by gaps,
which can be manipulated by external field. The Berry phase, related to the
motion of electrons in space, and the corresponding Chern numbers
characterizing topology of the energy bands are calculated analytically and
numerically. In this connection, we discuss the anomalous Hall effect in the
insulating state, when the Fermi level is located in the minigap. The results
of calculations show that in the model of gapless Dirac spectrum of graphene
the anomalous Hall effect can be treated as a sum of fractional quantum
numbers, related to the nonequivalent Dirac points.Comment: 6 pages, 5 figure
Density-matrix functionals for pairing in mesoscopic superconductors
A functional theory based on single-particle occupation numbers is developed
for pairing. This functional, that generalizes the BCS approach, directly
incorporates corrections due to particle number conservation. The functional is
benchmarked with the pairing Hamiltonian and reproduces perfectly the energy
for any particle number and coupling.Comment: 4 pages, 4 figures, revised versio
Anomalous Hall Effect due to the spin chirality in the Kagom\'{e} lattice
We consider a model for a two dimensional electron gas moving on a kagom\'{e}
lattice and locally coupled to a chiral magnetic texture. We show that the
transverse conductivity does not vanish even if spin-orbit
coupling is not present and it may exhibit unusual behavior. Model parameters
are the chirality, the number of conduction electrons and the amplitude of the
local coupling. Upon varying these parameters, a topological transition
characterized by change of the band Chern numbers occur. As a consequence,
can be quantized, proportional to the chirality or have a non
monotonic behavior upon varying these parameters.Comment: 8 pages, 7 figure
Functional approach for pairing in finite systems: How to define restoration of broken symmetries in Energy Density Functional theory ?
The Multi-Reference Energy Density Functional (MR-EDF) approach (also called
configuration mixing or Generator Coordinate Method), that is commonly used to
treat pairing in finite nuclei and project onto particle number, is
re-analyzed. It is shown that, under certain conditions, the MR-EDF energy can
be interpreted as a functional of the one-body density matrix of the projected
state with good particle number. Based on this observation, we propose a new
approach, called Symmetry-Conserving EDF (SC-EDF), where the breaking and
restoration of symmetry are accounted for simultaneously. We show, that such an
approach is free from pathologies recently observed in MR-EDF and can be used
with a large flexibility on the density dependence of the functional.Comment: proceeding of the conference "Many body correlations from dilute to
dense Nuclear systems", Paris, February 201
Description of Pairing correlation in Many-Body finite systems with density functional theory
Different steps leading to the new functional for pairing based on natural
orbitals and occupancies proposed in ref. [D. Lacroix and G. Hupin,
arXiv:1003.2860] are carefully analyzed. Properties of quasi-particle states
projected onto good particle number are first reviewed. These properties are
used (i) to prove the existence of such a functional (ii) to provide an
explicit functional through a 1/N expansion starting from the BCS approach
(iii) to give a compact form of the functional summing up all orders in the
expansion. The functional is benchmarked in the case of the picked fence
pairing Hamiltonian where even and odd systems, using blocking technique are
studied, at various particle number and coupling strength, with uniform and
random single-particle level spacing. In all cases, a very good agreement is
found with a deviation inferior to 1% compared to the exact energy.Comment: 14 pages, 9 figure
Kondo Screening and Magnetic Ordering in Frustrated UNi4B
UNi4B exhibits unusual properties and, in particular, a unique
antiferromagnetic arrangement involving only 2/3 of the U sites. Based on the
low temperature behavior of this compound, we propose that the remaining 1/3 U
sites are nonmagnetic due to the Kondo effect. We derive a model in which the
coexistence of magnetic and nonmagnetic U sites is the consequence of the
competition between frustration of the crystallographic structure and
instability of the 5f moments.Comment: 4 pages, 2 figure
Out of equilibrium transport through an Anderson impurity: Probing scaling laws within the equation of motion approach
We study non-equilibrium electron transport through a quantum impurity
coupled to metallic leads using the equation of motion technique at finite
temperature T. Assuming that the interactions are taking place solely in the
impurity and focusing in the infinite Hubbard limit, we compute the out of
equilibrium density of states and the differential conductance G_2(T,V) to test
several scaling laws. We find that G_2(T,V)/G_2(T,0) is a universal function of
both eV/T_K and T/T_K, being T_K the Kondo temperature. The effect of an in
plane magnetic field on the splitting of the zero bias anomaly in the
differential conductance is also analyzed. For a Zeeman splitting \Delta, the
computed differential conductance peak splitting depends only on \Delta/T_K,
and for large fields approaches the value of 2\Delta . Besides the traditional
two leads setup, we also consider other configurations that mimics recent
experiments, namely, an impurity embedded in a mesoscopic wire and the presence
of a third weakly coupled lead. In these cases, a double peak structure of the
Kondo resonance is clearly obtained in the differential conductance while the
amplitude of the highest peak is shown to decrease as \ln(eV/T_K). Several
features of these results are in qualitative agreement with recent experimental
observations reported on quantum dots.Comment: 9 pages, 7 figure
Coherence scale of the Kondo lattice
It is shown that the large-N approach yields two energy scales for the Kondo
lattice model. The single-impurity Kondo temperature, , signals the onset
of local singlet formation, while Fermi liquid coherence sets in only below a
lower scale, . At low conduction electron density
("exhaustion" limit), the ratio is much smaller than unity, and
is shown to depend only on and not on the Kondo coupling. The physical
meaning of these two scales is demonstrated by computing several quantities as
a function of and temperature.Comment: 4 pages, 4 eps figures. Minor changes. To appear in Phys. Rev. Let
Chiral two-dimensional electron gas in a periodic magnetic field
We study the energy spectrum and electronic properties of two-dimensional
electron gas in a periodic magnetic field of zero average with a symmetry of
triangular lattice. We demonstrate how the structure of electron energy bands
can be changed with the variation of the field strength, so that we can start
from nearly free electron gas and then transform it continuously to a system of
essentially localized chiral electron states. We find that the electrons near
some minima of the effective potential are responsible for occurrence of
dissipationless persistent currents creating a lattice of current contours. The
topological properties of the electron energy bands are also varied with the
intensity of periodic field. We calculated the topological Chern numbers of
several lower energy bands as a function of the field. The corresponding Hall
conductivity is nonzero and, when the Fermi level lies in the gap, it is
quantized.Comment: 10 pages;9 figures;42 reference
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