Magnetism and Superconductivity in a Two-band Hubbard Model in Infinite Dimensions

TL;DR

This paper investigates a two-band Hubbard model in infinite dimensions, revealing phase transitions between insulators, semimetals, and magnetic or superconducting states as electron density and interaction parameters vary.

Contribution

It provides a detailed analysis of phase transitions and magnetic/superconducting states in a two-band Hubbard model using dynamical mean-field theory with exact diagonalization.

Findings

Transition from band-insulator to correlated semimetal at n=2

Ferromagnetism and superconductivity emerge at low temperatures

Phase separation occurs between ferromagnetic and paramagnetic states

Abstract

We study a two-band Hubbard model using the dynamical mean-field theory combined with the exact diagonalization method. At the electron density $n=2$, a transition from a band-insulator to a correlated semimetal occurs when the on-site Coulomb interaction $U$ is varied for a fixed value of the charge-transfer energy $\Delta$. At low temperature, the correlated semimetal shows ferromagnetism or superconductivity. With increasing doping $|n-2|$, the ferromagnetic transition temperature rapidly decreases and finally becomes zero at a critical value of $n$. The second-order phase transition occurs at high temperature, while a phase separation of ferromagnetic and paramagnetic states takes place at low temperature. The superconducting transition temperature gradually decreases and finally becomes zero near $n=1$ ($n=3$) where the system is Mott insulator which shows antiferromagnetism at low temperature.