523 research outputs found
Electronic spectrum and superconductivity in the - model on the honeycomb lattice
A microscopic theory of electronic spectrum and superconductivity within the
- model on the honeycomb lattice is formulated. The Dyson equation for
the normal and anomalous Green functions for the two-band model in terms of the
Hubbard operators is derived by applying the Mori-type projection technique.
The self-energy is evaluated in the self-consistent Born approximation for
electron scattering on spin and charge fluctuations induced by the kinematical
interaction for the Hubbard operators. Superconducting pairing mediated by the
antiferromagnetic exchange and spin fluctuations is discussed.Comment: 11 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1803.0314
Superconductivity in the t-J model
A comparison of microscopic theories of superconductivity in the limit of
strong electron correlations is presented. We consider results for the
two-dimensional t-J model obtained within the projection technique for the
Green functions in terms of the Hubbard operators and the slave-fermion
representation for the RVB state. It is argued that the latter approach
resulting in the odd-symmetry p-wave pairing for fermions is inadequate.Comment: 11 pages, RevTex, 1 figure, to appear in Condensed Matter Physics
v.5, No.4 (2002)(Lviv, Ukraine) v.2: corrected typo
Spin fluctuations and high-temperature superconductivity in cuprates
To describe the cuprate superconductors, models of strongly correlated
electronic systems, such as the Hubbard or t-J models, are commonly employed.
To study these models, projected (Hubbard) operators have to be used. Due to
the unconventional commutation relations for the Hubbard operators, a specific
kinematical interaction of electrons with spin and charge fluctuations emerges.
The interaction is induced by the intraband hopping with a coupling parameter
of the order of the kinetic energy of electrons W which is much larger than the
antiferromagnetic exchange interaction J induced by the interband hopping. This
review presents a consistent microscopic theory of spin excitations and
superconductivity for cuprates where these interactions are taken into account
within the Hubbard operator technique. The low-energy spin excitations are
considered for the t-J model, while the electronic properties are studied using
the two-subband extended Hubbard model where the intersite Coulomb repulsion V
and electron-phonon interaction are taken into account.Comment: 26 pages, 33 figures, 130 references. arXiv admin note: text overlap
with arXiv:1301.4347, arXiv:1402.493
Optical and dc conductivities of cuprates: Spin-fluctuation scattering in the t-J model
A microscopic theory of the electrical conductivity within
the t-J model is developed. An exact representation for is
obtained using the memory-function technique for the relaxation function in
terms of the Hubbard operators, and the generalized Drude law is derived. The
relaxation rate due to the decay of charge excitations into particle-hole pairs
assisted by antiferromagnetic spin fluctuations is calculated in the
mode-coupling approximation. Using results for the spectral function of spin
excitations calculated previously, the relaxation rate and the optical and dc
conductivities are calculated in a broad region of doping and temperatures. The
reasonable agreement of the theory with experimental data for cuprates proves
the important role of spin-fluctuation scattering in the charge dynamics.Comment: 13 pages,15 figures, v.2, publication referenc
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