Quantum Monte Carlo and exact diagonalization study of a dynamic Hubbard model

Abstract

A one-dimensional model of electrons locally coupled to spin-1/2 degrees of freedom is studied by numerical techniques. The model is one in the class of dynamic Hubbard models that describe the relaxation of an atomic orbital upon double electron occupancy due to electron-electron interactions. We study the parameter regime where pairing occurs in this model by exact diagonalization of small clusters. World line quantum Monte Carlo simulations support the results of exact diagonalization for larger systems and show that kinetic energy is lowered when pairing occurs. The qualitative physics of this model and others in its class, obtained through approximate analytic calculations, is that superconductivity occurs through hole undressing even in parameter regimes where the effective on-site interaction is strongly repulsive. Our numerical results confirm the expected qualitative behavior, and show that pairing will occur in a substantially larger parameter regime than predicted by the approximate low energy effective Hamiltonian.

Magnetic ordering of itinerant systems: the role of kinetic interactions

“…For the curves of I cr ex (n) shown in Figs. 3 and 4 we assumed that S = S 1 [18]. In effect we obtained ∆t = t 0 (1 − S) and t ex = t 0 (1 − S) 2 2.…”

“…Parameter t 2 gives the hopping amplitude for an electron of spin σ when both sites i and j are occupied by electrons with opposite spin. Quite recently, several authors suggested that the expected relation t 0 > t 1 > t 2 , may be reversed for large enough inter-atomic distances, t 0 < t 1 < t 2 (see [13] and [18]). This concept would fit to the results of Gunnarsson and Christensen [19], who for the heavier elements (e.g.…”

Electron–Hole Asymmetry Driven Surface Charge Expulsion

“…For example, with both the IDHB and the twoband Hubbard model, it is also that the critical on-site Coulomb interaction (U c ) for a Mott metal-insulator transition is also stronger than that with the single-band Hubbard model. In the anti-adiabatic limit ω 0 → ∞, IDHB model modifies the Hubbard model with correlated hopping effective low energy Hamiltonian of which can be represented as follows [4]:…”

Photo-induced phase separation effect in cuprates

“…Depending on the parameters of the hole-configurational coupling and correlated hopping the modified Hubbard Hamiltonian (4) can stabilize the "disproportionated" or charge ordered (CO) electron phase with the on-site filling numbers n = 0, and n = 2 thus leading to the "negative-U" effect. Even simple modified model turns out to be very complicated and leads to a very rich physics [6]. Depending on the values of parameters the system yields the SDW phase with no core/shell displacements as a true ground state with a global minimum of free energy, and CO phase with shell displacements as a false ground state with a local minimum, or vice versa [7].…”

“…In particular, we should modify conventional Hubbard model as it is done, for instance, in a dynamic Hubbard model by Hirsch [6] and a modified Peierls-Hubbard model [7] with a classical description of the anharmonic core/shell displacements. Let address a square lattice Hubbard model with a half-filling and a strong on-site coupling of valent hole with core/shell displacements, which is described by the following Hamiltonian…”