MRSej, Vol. 6, No.1, pp.11-16, 2004
THE ISOTOPIC EFFECT IN HIGHLY CORRELATED SUPERCONDUCTORS
IN THE ANDERSON-HUBBARD TWO-ORBITAL MODEL
A.P. Achtanin, A.A. Kosov
Mari State University, Yoshkar-Ola, Mari El, 424001 Russia
The two-orbital
Hubbard model is used to obtain formula for the fermion
excitation spectrum in the energy bands hybridized by Anderson’s interaction. A transition
to the Hubbard operators diagonalizes the one-site
part of the Hamiltonian and allows us to use Green’s function technique to
take into account the interstitial hopping term, while studying the superconducting
properties of the model. By proposing the dependence of the matrix element
responsible for hybridization of p- and d- electronic states
on the ampltitude of local vibrations of ions, we
determined a value of isotopic effect a = ( M / Tc ) ( dTc / dM )
(M – mass of ions). The dependence of a upon carrier
density and energy parameters determining the intra-atomic correlation is
analyzed. It was concluded, that at some values of parameters the isotopic
effect in Tc can be large enough and the model under consideration
can be used for the description of the isotopic shift in Tc for a number of superconductors.
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