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arXiv:cond-mat/9412109 · Journal of Physics Condensed Matter

Metal-insulator transition in the generalized Hubbard model

A A Ovchinnikov

Published Dec 12, 1994• 9 citations
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Abstract

We present the exact ground-state wave function and energy of the generalized Hubbard model, subject to the condition that the number of doubly occupied sites is conserved. For a wide, physically relevant range of parameters. For one hole and one doubly occupied site the existence of the ferromagnetic ground state is proved which allows one to determine the critical value of the on-site repulsion corresponding to the point of metal-insulator transition. For the one-dimensional model the exact solution for special values of the parameters is obtained.

DOI
10.1088/0953-8984/6/50/015

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We present the exact ground-state wave function and energy of the generalized Hubbard model, subject to the condition that the number of doubly occupied sites is conserved. For a wide, physically relevant range of parameters. For one hole and one doubly occupied site the existence of the ferromagnetic ground state is proved which allows one to determine the critical value of the on-site repulsion corresponding to the point of metal-insulator transition. For the one-dimensional model the exact solution for special values of the parameters is obtained.
We present the exact ground-state wave function and energy of the generalized Hubbard model, subjected to the condition that the number of double occupied sites is conserved, for a wide, physically relevant range of parameters. For one hole and one double occupied site the existence of the ferromagnetic ground-state is proved which allow one to determine the critical value of the on-site repulsion corresponding to the point of metal-insulator transition. For the one dimensional model the exact solution for special values of the parameters is obtained. 1
We study a generalized Hubbard model with on-site interaction U, nearest-neighbor repulsion V, and general correlated hopping under the condition that the number of doubly occupied sites is conserved. We find the exact ground state (GS) in arbitrary dimension in two wide regions of parameters. In one of them the GS is a Mott insulator (MI) and in the other it is a charge-density wave (CDW). The boundary of the MI and a large part of that of the CDW are determined exactly for relevant lattices. We study numerically the effect of relaxing the above-mentioned condition.
We investigate the ground state (T = 0 K) of the one-dimensional symmetrical (n = 1) Hubbard model formalized in terms of the system of integral equations, which we previously obtained using the method of the generating functional of Green’s functions with the subsequent Legendre transformation. In a wide range of variations in the parameter of Coulomb interaction U, the following characteristics of the system have been calculated: the electron density of states, the electron band spectrum, the number of doubly occupied lattice sites, the localized magnetic moment, the correlator of the square of the longitudinal component of spin at a site,<S Z 2>, and the internal energy of the system. It has been shown that, for all U > 0, the model yields two solutions, i.e., an antiferromagnetic insulator and a paramagnetic insulator, in which there are no single-electron quasi-particles at the Fermi level. The energy of the paramagnetic solution in the region of U < 1.1 is considerably less than that of the antiferromagnetic solution for the case of U > 1.1, we have the opposite situation.
The Mott-Hubbard transition is studied in the context of the two-dimensional Hubbard model. Analytical calculations show the existence of a critical value Uc of the potential strength which separates a paramagnetic metallic phase from a paramagnetic insulating phase. Calculations of the density of states and double occupancy show that the ground state in the insulating phase contains always a small fraction of empty and doubly occupied sites. The structure of the ground state is studied by considering the probability amplitude of intersite hopping. The results indicate that the ground state of the Mott insulator is characterized by a local antiferromagnetic order; the electrons keep some mobility, but this mobility must be compatible with the local ordering. The vanishing of some intersite probability amplitudes at U=Uc puts a constrain on the electron mobility. It is suggested that such quantities might be taken as the quantities which control the order in the insulating phase.
We study the metal-insulator transition of the d-dimensional Hubbard model by treating the hopping term between adjacent 1-d chains in the frame of a Clifford linearization scheme, and keeping the full model along the chains. A general equation for the critical point is worked out in terms of the correlation functions of the one-dimensional model, assuming that the transition is of the second order. The equation, which holds at any temperature, is here investigated especially at T=0, where the latter condition holds true. The solution shows the existence of an insulating ground state in any d only at half-filling for U strictly positive, as in the exact 1-d case. The transition is found to be related to a parameter reminiscent of entropy.