Ground-State Properties of the Hubbard Model with Modified Band Structure and Extended Electron Interactions^

Shiwei Zhang, Ettore Vitali, Adam Chiciak +1 more

Allman, Eric

We present results from a constrained path Monte Carlo (CPMC) study of a modified two-dimensional Hubbard model. We include more general forms of the band structure and electron interaction in order to examine their effects on ground-state properties, such as electron pairing correlations. Both next-nearest neighbor hopping, t', and third-nearest neighbor hopping, t″, are introduced in the Hamiltonian. A nearest neighbor interaction of strength V is also included. We carry out CPMC calculations on system sizes up to 16 x 16, at various electron fillings, to investigate the ground state of the model for different values of these parameters. For realistic systems, these calculations indicate that Hubbard-like models are not capable of showing enhanced pairing. The modified Hamiltonian also presents an opportunity to more closely examine the accuracy and robustness of the CPMC algorithm. Results of further benchmark calculations involving CPMC are presented. These benchmarks confirm that CPMC is able to show enhanced pairing in systems where such behavior is known to exist.

Eli Eisenberg, Richard Berkovits

Abstract. We study the influence of on-site disorder on the magnetic properties of the ground state of the infinite-U one-dimensional (1D) Hubbard model. We find that the ground state is not ferromagnetic. This is analysed in terms of the algebraic structure of the spin dependence of the Hamiltonian. A simple explanation is derived for the 1=N periodicity in the persistent current for this model. The Hubbard model is the simplest model one can study to examine the effects of correlations between electrons in narrow energy bands. The Hamiltonian consists of a nearest neighbour hopping term and an electron–electron repulsion, U, which acts only when two electrons are on the same site. The Hubbard model is also the canonical model for the study of itinerant ferromagnetism. The strong coupling regime is of special importance for the study of ferromagnetism, since a theorem by Nagaoka [1] states that in theU D 1 limit, the ground state (GS) is ferromagnetic given some connectivity property of the lattice (which holds in most cases for d> 1). The model is solvable in one dimension and it was shown [2] that for open boundary conditions (BCs) the GS for finiteU is a singlet, i.e. there can be no ferromagnetism unless one postulates explicitly spin- or velocity-dependent forces. For infinite U, the GS of

Tomotoshi Nishino

U. Brandt, Joachim Stolze

Anatoliy F. Zhuravlyov

A simple way to determine the channel of scattering of the Hubbard chain electrons with additional quantum number, which means the orbital or band characteristic, is demonstrated on the integrable 1D modified Hubbard model. Exact solutions are obtained for each scattering channel of the electrons. The preferable channel is determined by means of numerical calculations of the ground-state energies and comparison its values. The dependence of the scattering matrices on the parameters of Coulomb, orbital (band), and spin interactions gives the possibility to present the properties of the system considered in different ranges (reasonable in physics sense) of parameters which correspond to the electron coupling. The ratio between magnetic susceptibility and heat capacity of the model is presented.