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Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics

First-order phase transitions in the Montorsi-Rasetti model

Kristel F. L. Michielsen, Hans A. De Raedt

Published Dec 1, 1994• 1 citation
Publisher

Abstract

Exact diagonalization and quantum Monte Carlo methods are used to explore the zero-temperature phase diagram of a simplified Hubbard model extended with bond-charge--site-charge interactions. Numerical results for the grand potential and for its first derivatives with respect to the Coulomb potential and the chemical potential strongly suggest the occurrence of first-order phase transitions. It is shown that there is a close analogy between the first-order ground-state phase transitions in this quantum system and the phase transitions in classical (P,V,T) systems.

DOI
10.1103/physreve.50.4371

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Exact diagonalization and quantum Monte Carlo methods are used to explore the zero-temperature phase diagram of a simplified Hubbard model extended with bond-charge--site-charge interactions. Numerical results for the grand potential and for its first derivatives with respect to the Coulomb potential and the chemical potential strongly suggest the occurrence of first-order phase transitions. It is shown that there is a close analogy between the first-order ground-state phase transitions in this quantum system and the phase transitions in classical (P,V,T) systems.
An overview of lattice models for strongly correlated electrons is given. A detailed study is presented of a model recently introduced by Montorsi and Rasetti. Analytical, exact diagonalization and Quantum Monte Carlo techniques are employed to investigate the static and dynamic properties of this model. The complete ground state phase diagram of the one-, two- and three-dimensional model is given. The Montorsi-Rasetti model is shown to exhibit a metal-insulator transition of the Mott type, independent of the dimensionality of the lattice, and has a ferromagnetic phase. Results for the two-dimensional Montorsi-Rasetti model strongly suggest the occurrence of a phase transition at finite temperatures.
Exact-diagonalization and quantum Monte Carlo methods are used to study the occurrence of a metal-insulator transition and the distribution of charges and magnetic moments in the ground state of a one- and two-dimensional half-filled system of correlated electrons, described by a one-band simplified Hubbard model extended with bond-charge--site-charge interactions. Numerical results for the electrical conductivity, the density of states, and the spin- and charge-density correlation functions strongly suggest that the bond-charge--site-charge interaction plays a fundamental role in the occurrence of a metal-insulator transition and of ferromagnetic order.
Similar quantum phase diagrams and transitions are found for three classes of one-dimensional models with equally spaced sites, singlet ground states (GS), inversion symmetry at sites and a bond order wave (BOW) phase in some sectors.The models are frustrated spin-1/2 chains with variable range exchange, half-filled Hubbard models with spin-independent interactions and modified Hubbard models with site energies for describing organic charge transfer salts.In some range of parameters, the models have a first order quantum transition at which the GS expectation value of the sublattice spin S A 2  of odd or even-numbered sites is discontinuous.There is an intermediate BOW phase for other model parameters that lead to two continuous quantum transitions with continuous S A 2 .Exact diagonalization of finite systems and symmetry arguments provide a unified picture of familiar 1D models that have appeared separately in widely different contexts.(