Some finite temperature and ground state properties of high-Tc superconductivity within the planar t-J-U model

Abstract

In high-Tc materials, considering pair hopping and on-site pairing of electrons, presence of two electrons at a site following Pauli exclusion principle (a t-J-U model) is relevant. Considering this novelty, within a two-dimensional (2D) t-J-U Hamiltonian, some thermodynamic and ground state properties of high-Tc cuprates at various hole doping concentrations (〈h〉) have been investigated. Any theory based on perturbation approximation is inapplicable in strongly correlated electron systems, therefore, Lanczos method of exact diagonalization on a square cluster (tilted) of 8-sites is followed. Results show that double occupancy (δ) is maximum for hole concentration 〈h〉 = 0.25 and increases at a particular temperature T = T(U). Local moment shows the opposite behavior. Spin-spin correlation is negative between nearest-neighbor sites, confirming antiferromagnetic nature of the system. It appears that on-site Coulomb repulsion (U/t ≥ 6.0) destabilizes the superconducting ground state. In the system, antiferromagnetism (AF) and superconductivity are seen to coexist. A uniform distribution of charges is seen with increasing on-site Coulomb repulsion (U), which results in constant electron–electron correlation.