Altermagnetic ferroelectric LiFe2F6 and spin-triplet excitonic insulator phase

TL;DR

This paper predicts that LiFe2F6 is an altermagnetic ferroelectric material with potential for spintronic applications, exhibiting a spin-triplet excitonic insulator phase and strong magnetoelectric coupling.

Contribution

It introduces LiFe2F6 as a novel altermagnetic ferroelectric with unique spin and electric properties, including a switchable spin-triplet excitonic insulator phase.

Findings

LiFe2F6 is a d-wave altermagnetic ferroelectric.

Under strain, it becomes ferrimagnetic and ferroelectric with magnetoelectric coupling.

It hosts a spin-triplet excitonic insulator phase with electric field switchability.

Abstract

Altermagnetism is a new magnetic phase with k-dependent spin polarization and may exist in an insulating state with a high N\'eel temperature. This provides a new opportunity to obtain both spin and electric polarization in one material. Here, based on symmetry analysis and the first-principles electronic structures calculations, we predict that LiFe2F6 is a d-wave altermagnetic and charge-ordering-mediated ferroelectric material. Moreover, the LiFe2F6 transforms into a ferrimagnetic and ferroelectric phase with strong magnetoelectric coupling under biaxial compressive strain. Interestingly, the spins of the valence band and the conduction band are opposite in ferrimagnetic LiFe2F6, which facilitates a simultaneous spin-triplet excitonic insulator phase. More importantly, the spin-triplet excitons with spin 1 and -1 can be switched by electric fields in ferrimagnetic LiFe2F6 due to strong magnetoelectric coupling. Due to the abundance of novel physical properties, LiFe2F6 will certainly attract a wide range of theoretical and experimental interest.