Antiferromagnetic ground state with pair-checkboard order in FeSe

TL;DR

This paper discovers a new magnetic ground state called 'pair-checkboard AFM' in FeSe, which is insulating with a Dirac-like band structure, providing insights into its superconductivity and contrasting previous assumptions of a stripe AFM order.

Contribution

The study identifies a novel magnetic order in FeSe, challenging prior models and revealing its insulating nature with a unique band structure linked to orbital order.

Findings

Discovery of pair-checkboard AFM as the ground state in FeSe.

Monolayer FeSe exhibits insulating behavior with Dirac-cone-like bands.

The magnetic order results from complex exchange interactions among Fe atoms.

Abstract

Monolayer FeSe thin film grown on SrTiO_{3}(001) (STO) shows the sign of T_{c}> 77 K, which is higher than the T_{c}-record of 56 K for the bulk FeAs-based superconductors. However, little is known about the magnetic ground state of FeSe, which should be closely related to its unusual superconductivity. Previous studies presume the collinear stripe antiferromagnetic (AFM) state as the ground state of FeSe, same to that in FeAs superconductors. Here we find a novel magnetic order named "pair-checkboard AFM" as the magnetic ground state of tetragonal FeSe. The novel pair-checkboard order results from the interplay between the nearest, the next-nearest and the unnegligible next-next-nearest neighbor magnetic exchange couplings of Fe atoms. The monolayer FeSe in pair-checkbord order shows an unexpected insulating behavior with a Dirac-cone-like band structure related to the specific orbital order of d_{xz} and d_{yz} characters of Fe atoms, which could explain recently observed insulator-superconductor transition. The present results cast new insights on the magnetic ordering in FeSe monolayer and its derived superconductors.