Some thermodynamic non-Fermi liquid properties of correlated electron systems. (...)Cu_<i>m</i>O<sub><i>n-x</i><sub>

Abstract

A mean-field Hamiltonian model has been used to investigate some thermodynamic properties of the normal states of non-Fermi liquid (NFL) systems,(...)Cu_mO<sub>n-x . This Hamiltonian is like that of the Bardeen-Cooper-Schrieffer model [Phys. Rev. 108 (1957) 1175] but differs from the latter in (i) being multiband, (ii) the gap in energy being a function of the hopping integral and (iii) band energies of electrons being dependent upon spin orientation. The Hamiltonian is, therefore, similar to the Paring t-model [Physica 258 (9166) 30] but differs from it in not incorporating hybridization term and hybrid pair superconductivity. The analysis of the model yields magnetic energy spectrum for Cu (3d) bands` and non-magnetic energy spectrum for the O (2p) bands. Inverse temperature dependences of electronic specific heat Cv , entropy function (S) and pair susceptibility (Χ↑↓) are computed and exhibited. The specific heat dependence upon inverse temperature shows a linear form at very high temperature. It displays inverse-square-law temperature dependence, approximately, for lower temperatures. In the very low temperature range, the actual curve of the theoretical specific heat with temperature is rather like that of the Cp versus T^-2 curve obtained for Bi4Cu4O16+y and Ti2Ba2Cn-1CunO2n+4 down to millikelvin temperature. This is in contradistinction to the linear temperature dependence (Cv = γT) of Fermi liquid systems. The specific entropy dependence on temperature shows correct physical response of systems to order (disorder) with varying temperatures. The pair susceptibility is linear at very high temperature and constant (X=X0) at moderate/low temperatures. The latter is as in Fermi liquid systems, but the former is an NFL manifestation.

Journal of the Nigerian Association of Mathematical Physics Vol. 10 2006: pp. 149-156</sub>