179 research outputs found
The representations of the Hubbard algebra in terms of spin-fermion operators and motion of a hole in an antiferromagnetic state
The representation of the Hubbard operators in terms of the
spin operators and the fermion operator with spin
is proposed.
In the low-energy limit this representation is reduced to the representation
following from the Hubbard diagramm technique. In framework of this approach
motion of a hole in an antiferromagnetic state of the t-J model is considered.
It is shown that the primary hole energy is strongly renormalized and the band
width has an order of J rather than t.
The functional integral for the strongly correlated model induced by the
obtained representation is formulated. The representation of the total Hubbard
algebra for states in the lower and the upper Hubbard bands is formulated in
terms of the spin and two fermion fields with spin
is formulated.Comment: 12 pp. (LATEX
Multiscale velocity correlation in turbulence: experiments, numerical simulations, synthetic signals
Multiscale correlation functions in high Reynolds number experimental
turbulence, numerical simulations and synthetic signals are investigated.
Fusion Rules predictions as they arise from multiplicative, almost
uncorrelated, random processes for the energy cascade are tested. Leading and
sub-leading contribution, in the inertial range, can be explained as arising
from a multiplicative random process for the energy transfer mechanisms. Two
different predictions for correlations involving dissipative observable are
also briefly discussed
Rectification in Luttinger liquids
We investigate the rectification of an ac bias in Luttinger liquids in the
presence of an asymmetric potential (the ratchet effect). We show that strong
repulsive electron interaction enhances the ratchet current in comparison with
Fermi liquid systems, and the I-V curve is strongly asymmetric in the
low-voltage regime even for a weak asymmetric potential. At higher voltages the
ratchet current exhibits an oscillatory voltage dependence.Comment: 5 pages, Revte
Nonequilibrium charge dynamics of light-driven rings threaded by a magnetic flux
We study theoretically the charge polarization and the charge current
dynamics of a mesoscopic ring driven by short asymmetric electromagnetic pulses
and threaded by an external static magnetic flux. It is shown that the
pulse-induced charge polarization and the associated light-emission is
controllable by tuning the external magnetic flux. Applying two mutually
perpendicular pulses triggers a charge current in the ring. The interplay
between this nonequilibrium and the persistent currents is investigated and the
conditions under which the pulses stop the persistent current are identified.Comment: 6 pages, 2 figures; submitted to EP
Analytic and geometric properties of photoinduced effects in noncentrosymmetric crystals: photovoltaic current and optical rectification
An original dispersion relation between the stationary coherent nonlinear
optical responses by current and polarisation is obtained. The dispersion
relation provides a new complimentary tool that can be employed to study
light-induced charge transport models and facilitate experimental data
analysis. It is shown that the origin of the coherent current and the
dc-polarisation induced in a noncentrosymmetric crystal under illumination is
related to the theory of the Berry phase and can be represented in terms of the
renormalised geometric potentials. This renormalisation originates from the
extra phase difference acquired by a carrier in the light field on the quantum
transition between the electronic bands. The gauge invariance of the
corresponding expressions for the current and the polarisation is demonstrated.Comment: 7 page
Charge and spin Hall conductivity in metallic graphene
Graphene has an unusual low-energy band structure with four chiral bands and
half-quantized and quantized Hall effects that have recently attracted
theoretical and experimental attention. We study the Fermi energy and disorder
dependence of its spin Hall conductivity. In the metallic regime we find that
vertex corrections enhance the intrinsic spin Hall conductivity and that skew
scattering can lead to its values that exceed the quantized ones expected when
the chemical potential is inside the spin-orbit induced energy gap. We predict
that large spin Hall conductivities will be observable in graphene even when
the spin-orbit gap does not survive disorder.Comment: 4 pages, 2 figure
Correlation functions in isotropic and anisotropic turbulence: the role of the symmetry group
The theory of fully developed turbulence is usually considered in an
idealized homogeneous and isotropic state. Real turbulent flows exhibit the
effects of anisotropic forcing. The analysis of correlation functions and
structure functions in isotropic and anisotropic situations is facilitated and
made rational when performed in terms of the irreducible representations of the
relevant symmetry group which is the group of all rotations SO(3). In this
paper we firstly consider the needed general theory and explain why we expect
different (universal) scaling exponents in the different sectors of the
symmetry group. We exemplify the theory context of isotropic turbulence (for
third order tensorial structure functions) and in weakly anisotropic turbulence
(for the second order structure function). The utility of the resulting
expressions for the analysis of experimental data is demonstrated in the
context of high Reynolds number measurements of turbulence in the atmosphere.Comment: 35 pages, REVTEX, 1 figure, Phys. Rev. E, submitte
Quantum kinetic theory of shift current electron pumping in semiconductors
We develop a theory of laser beam generation of shift currents in
non-centrosymmetric semiconductors. The currents originate when the excited
electrons transfer between different bands or scatter inside these bands, and
asymmetrically shift their centers of mass in elementary cells. Quantum kinetic
equations for hot-carrier distributions and expressions for the induced
currents are derived by nonequilibrium Green functions. In applications, we
simplify the approach to the Boltzmann limit and use it to model laser-excited
GaAs in the presence of LO phonon scattering. The shift currents are calculated
in a steady-state regime.Comment: 23 pages, 5 figures (Latex
Hole-hole superconducting pairing in the t-J model induced by spin-wave exchange
We study numerically the hole pairing induced by spin-wave exchange. The
contact hole-hole interaction is taken into account as well. It is assumed that
antiferromagnetic order is preserved at all scales relevant to pairing. The
strongest pairing is obtained for the d-wave symmetry of the gap. Dependence of
the value of the gap on hole concentration and temperature is presented. For
the critical temperature we obtain Tc about 100 K at the hole concentration
delta = 0.2-0.3.Comment: replaced with a revised version to appear in PRB, 6 pages, REVTeX
3.0, figures not change
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