Orbital order and fluctuations in the two-leg ladder materials ${\mathrm{BaFe}}_{2}{X}_{3}$ ($X=\mathrm{S}$ and Se) and ${\mathrm{CsFe}}_{2}{\mathrm{Se}}_{3}$

Orbital order and fluctuations in the two-leg ladder materials ${BaFe}_{2} X_{3}$ ( $X = S$ and Se) and ${CsFe}_{2} {Se}_{3}$

Kou Takubo, Yuichi Yokoyama, Hiroki Wadati, Shun Iwasaki, Takashi Mizokawa, Teak Boyko, Ronny Sutarto, Feizhou He, Kazuki Hashizume, Satoshi Imaizumi, Takuya Aoyama, Yoshinori Imai, and Kenya Ohgushi

Phys. Rev. B 96, 115157 – Published 27 September 2017

Abstract

The electronic structure of ${BaFe}_{2} X_{3}$ ( $X$ = S and Se) and ${CsFe}_{2} {Se}_{3}$ in which two-leg ladders are formed by the Fe sites are studied by means of x-ray absorption and resonant inelastic x-ray scattering spectroscopy. The x-ray absorption spectra at the Fe $L$ edges for ${BaFe}_{2} X_{3}$ exhibit two components, indicating that itinerant and localized Fe $3 d$ sites coexist. Substantial x-ray linear dichroism is observed in polarization dependent spectra, indicating the existence of orbital order or fluctuation in the Fe ladder even above the Néel temperature $T_{N}$ . Direct exchange interaction along the legs of the Fe ladder stabilizes the orbital and antiferromagnetic orders in ${BaFe}_{2} S_{3}$ , while the ferromagnetic molecular orbitals are realized between the rungs in ${CsFe}_{2} {Se}_{3}$ .