Magnetic field effects in a correlated electron system with spin-state degree of freedom - Implication of an excitonic insulator -

TL;DR

This paper investigates how magnetic fields influence a correlated electron system with spin-state degrees of freedom, revealing phase transitions including excitonic insulator and spin-state order, with complex phase diagrams analyzed via mean-field approximation.

Contribution

It introduces a theoretical analysis of magnetic field effects on spin-state degrees of freedom using an effective Hamiltonian derived from a two-orbital Hubbard model.

Findings

Magnetic field induces excitonic insulating and spin-state ordered phases.

Reentrant transition observed in high-spin phase under magnetic field.

Complex phase diagrams depend on spin-state configurations and interactions.

Abstract

Magnetic field (H) effects on a correlated electron system with the spin-state degree of freedom are examined. The effective Hamiltonian derived from the two-orbital Hubbard model is analyzed by the mean-field approximation. Applying H to the low-spin (LS) phase induces the excitonic insulating phase, as well as the spin-state ordered phase where the LS and high-spin (HS) states are ordered alternately. In the case where H is applied to the HS phase, a reentrant transition for the HS phase appears. A rich variety of the phase diagrams are attributed to the spin-state degree of freedom and their combinations in the wave function as well as in the real-space configuration.