Spin and charge modulations of a half-filled extended Hubbard model

TL;DR

This paper investigates an extended Hubbard model on a square lattice at half filling, revealing complex charge and spin modulations, phase boundaries, and transitions influenced by a staggered local potential, with implications for resistive switching.

Contribution

It introduces and analyzes a model with intersite Coulomb interaction and staggered local potential, identifying new charge and spin order phases and their transitions.

Findings

Charge order (CO) and joint spin-charge modulations (SCO) are stabilized at finite SLP.

Phase boundaries and order parameter variations are mapped out.

Coexistence domains of CO and SCO are identified, relevant for resistive switching.

Abstract

We introduce and analyze an extended Hubbard model, in which intersite Coulomb interaction as well as a staggered local potential (SLP) are considered, on the square lattice at half band filling, in the thermodynamic limit. Using both Hartree-Fock approximation and Kotliar and Ruckenstein slave boson formalism, we show that the model harbors charge order (CO) as well as joint spin and charge modulations (SCO) at finite values of the SLP, while the spin density wave (SDW) is stabilized for vanishing SLP, only. We determine their phase boundaries and the variations of the order parameters in dependence on the SLP, as well as on the on-site and nearest-neighbor interactions. Domains of coexistence of CO and SCO phases, suitable for resistive switching experiments, are unraveled. We show that the novel SCO systematically turns into the more conventional SDW phase when the zero-SLP limit is taken. We also discuss the nature of the different phase transitions, both at zero and finite temperature. In the former case, no continuous CO to SDW (or SCO) phase transition occurs. In contrast, a paramagnetic phase (PM), which is accompanied with continuous phase transitions towards both spin or charge ordered phases, sets in at finite temperature. A good quantitative agreement with numerical simulations is demonstrated, and a comparison between the two used approaches is performed.