443 research outputs found
Thermodynamics of symmetric spin--orbital model: One- and two-dimensional cases
The specific heat and susceptibilities for the two- and one-dimensional
spin--orbital models are calculated in the framework of a spherically symmetric
self-consistent approach at different temperatures and relations between the
parameters of the system. It is shown that even in the absence of the
long-range spin and orbital order, the system exhibits the features in the
behavior of thermodynamic characteristics, which are typical of those
manifesting themselves at phase transitions. Such features are attributed to
the quantum entanglement of the coupled spin and orbital degrees of freedom.Comment: 7 pages, 9 figures, submitted to JETP Letter
Neutrino scattering on polarized electron target as a test of neutrino magnetic moment
We suggest to use a polarized electron target for improving the sensitivity
of the search for the neutrino magnetic moment to the level in the processes of neutrino (antineutrino) -- electron
scattering. It is shown that in this case the weak interaction term in the
total cross section is significantly suppressed comparing with unpolarized
case, but the electromagnetic term does not depend on electron polarization.Comment: 11 pages, LaTeX2e, using elsart.cls and epsf.sty, 3 postscript
figures. Accepted in Phys. Lett.
Electrical resistivity, hall coefficient, and thermopower of optimally doped high-T c superconductors
© 2014, Pleiades Publishing, Inc. For a two-dimensional optimally doped antiferromagnet with spin S =1/2, we study the temperature dependence of the electrical resistivity Ï(T), Hall coefficient RH(T), and thermopower Q(T). The temperature dependence corresponding to optimally doped layered high-Tc superconducting cuprates has been obtained simultaneously for all three transport coefficients within the unified spin-polaron approach for the Kondo lattice. The key features of our study are the usage of the multimoment method for solving the kinetic equations (seven moments for the nonequilibrium distribution function ensure a good convergence) and the form of ac spin susceptibility Ï(q, Ï) for localized spins. For Ï(q, Ï), we choose a self-consistent expression which takes into account the âcrossoverâ between the spin susceptibility determined by the self-consistent spherically symmetric Greenâs function method and the semiphenomenological spin susceptibility corresponding to the critical decay of magnons
Many-Body Approch to Spin-Dependent Transport in Quantum Dot Systems
By means of a diagram technique for Hubbard operators we show the existence
of a spin-dependent renormalization of the localized levels in an interacting
region, e.g. quantum dot, modeled by the Anderson Hamiltonian with two
conduction bands. It is shown that the renormalization of the levels with a
given spin direction is due to kinematic interactions with the conduction
sub-bands of the opposite spin. The consequence of this dressing of the
localized levels is a drastically decreased tunneling current for
ferromagnetically ordered leads compared to that of paramagnetically ordered
leads. Furthermore, the studied system shows a spin-dependent resonant
tunneling behaviour for ferromagnetically ordered leads.Comment: 8 pages, 5 figure
Dispersion of the dielectric function of a charge-transfer insulator
We study the problem of dielectric response in the strong coupling regime of
a charge transfer insulator. The frequency and wave number dependence of the
dielectric function and its inverse is the main object of consideration. We show that the
problem, in general, cannot be reduced to a calculation within the Hubbard
model, which takes into account only a restricted number of electronic states
near the Fermi energy. The contribution of the rest of the system to the
longitudinal response (i.e. to ) is essential
for the whole frequency range. With the use of the spectral representation of
the two-particle Green's function we show that the problem may be divided into
two parts: into the contributions of the weakly correlated and the Hubbard
subsystems. For the latter we propose an approach that starts from the
correlated paramagnetic ground state with strong antiferromagnetic
fluctuations. We obtain a set of coupled equations of motion for the
two-particle Green's function that may be solved by means of the projection
technique. The solution is expressed by a two particle basis that includes the
excitonic states with electron and hole separated at various distances. We
apply our method to the multiband Hubbard (Emery) model that describes layered
cuprates. We show that strongly dispersive branches exist in the excitonic
spectrum of the 'minimal' Emery model () and consider the
dependence of the spectrum on finite oxygen hopping and on-site
repulsion . The relationship of our calculations to electron energy loss
spectroscopy is discussed.Comment: 22 pages, 5 figure
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