Coexistence of localized and itinerant electrons in BaFe2X3 (X = S and Se) revealed by photoemission spectroscopy

TL;DR

This study uses photoemission spectroscopy to reveal the coexistence of localized and itinerant electrons in BaFe2X3 (X = S, Se) and CsFe2Se3, highlighting their electronic structure and insulating behavior.

Contribution

It provides new insights into the electronic states of BaFe2X3 and CsFe2Se3, showing coexistence of localized and itinerant electrons and characterizing their ground states.

Findings

Coexistence of localized and itinerant Fe 3d electrons in BaFe2X3.

CsFe2Se3 exhibits a sharp Fe 2p core-level peak with charge-transfer satellite.

CsFe2Se3 is a Fe2+ Mott insulator despite a +2.5 valence.

Abstract

We report a photoemission study at room temperature on BaFe2X3 (X = S and Se) and CsFe2Se3 in which two-leg ladders are formed by the Fe sites. The Fe 2p core-level peaks of BaFe2X3 are broad and exhibit two components, indicating that itinerant and localized Fe 3d sites coexist similar to KxFe2-ySe2. The Fe 2p core-level peak of CsFe2Se3 is rather sharp and is accompanied by a charge-transfer satellite. The insulating ground state of CsFe2Se3 can be viewed as a Fe2+ Mott insulator in spite of the formal valence of +2.5. The itinerant versus localized behaviors can be associated with the stability of chalcogen p holes in the two-leg ladder structure.