Magnetism and Mott Transition: A Slave-rotor Study

TL;DR

This study uses a slave-rotor mean-field approach to explore the interplay of magnetism and Mott transition in a two-band Hubbard model relevant to iron-based superconductors, revealing distinct regimes of first-order transitions and local-moment physics.

Contribution

It introduces a slave-rotor mean-field method to analyze the phase diagram of a two-band Hubbard model with Fermi surface nesting, highlighting the role of Hund's coupling in magnetic and Mott transitions.

Findings

Mott transition can be strongly first-order for certain Hund's couplings.

Enhanced magnetization observed near the SDW phase at stronger Hund's coupling.

Some FeSC materials may be close to the regime showing signs of local-moment physics.

Abstract

Motivated by the debate of spin-density-wave (SDW) versus local-moment (LM) picture in the iron-based superconducting (FeSC) materials, we consider a two-band orbital-symmetric Hubbard model in which there is robust Fermi surface nesting at $(\pi,0)$. We obtain the phase diagram of such system by a mean-field slave-rotor approach, in which the Fermi surface nesting and the SDW order are explicitly taken into account via a natural separation of scale between the Hund's coupling and the Coulomb interaction. We find that for a sizable range of Hund's coupling the Mott transition acquires a strong first-order character, but there also exists a small range of stronger Hund's coupling in which an enhancement of magnetization can be observed on the SDW side. We interpret the former scenario as one in which a sharp distinction can be drawn between LM and the SDW picture, and the latter scenario as one in which signs of LM physics begin to develop in the metallic phase. It is tempting to suggest that some FeSC materials are in the vicinity of the latter scenario.