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An exact study of charge-spin separation, pairing fluctuations and pseudogaps in four-site Hubbard clusters

Armen N. Kocharian·Gayanath W. Fernando·Kalum Palandage·James W. Davenport
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Abstract

An exact study of charge-spin separation, pairing fluctuations and pseudogaps is carried out by combining the analytical eigenvalues of the four-site Hubbard clusters with the grand canonical and canonical ensemble approaches in a multidimensional parameter space of temperature (T), magnetic field (h), on-site interaction (U) and chemical potential. Our results, near the average number of electrons =3, strongly suggest the existence of a critical parameter U_{c}(T) for the localization of electrons and a particle-hole binding (positive) gap at U>U_{c}(T), with a zero temperature quantum critical point, U_{c}(0)=4.584. For U U_c(T) and the cluster becomes a Mott-Hubbard like insulator due to the presence of energy gaps at all (allowed) integer numbers of electrons. In contrast, for U< U_c(T), we find an electron pair binding instability at finite temperature near =3, which manifests a possible pairing mechanism, a precursor to superconductivity in small clusters. In addition, the resulting phase diagram consisting of charge and spin pseudogaps, antiferromagnetic correlations, hole pairing with competing hole-rich ( =2), hole-poor ( =4) and magnetic ( =3) regions in the ensemble of clusters near 1/8 filling closely resembles the phase diagrams and inhomogeneous phase separation recently found in the family of doped high T_c cuprates.

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Armen N. Kocharian, Gayanath W. Fernando, Kalum Palandage, James W. Davenport. 2006-06-07. An exact study of charge-spin separation, pairing fluctuations and pseudogaps in four-site Hubbard clusters. https://doi.org/10.1103/physrevb.74.024511

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