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$-\frac{1}{2}$ operators and the fermion operator with spin$-\frac{1}{2}$ 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$-\frac{1}{2}$ and two fermion fields with spin$-\frac{1}{2}$ 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