Resonant inelastic x-ray scattering study of electronic excitations in insulating K$_{0.83}$Fe$_{1.53}$Se$_2$

TL;DR

This study uses resonant inelastic X-ray scattering to investigate electronic excitations in insulating K$_{0.83}$Fe$_{1.53}$Se$_2$, revealing momentum-dependent features linked to correlated Fe 3d electrons and suggesting similar electron correlations in related superconductors.

Contribution

First RIXS investigation of insulating K$_{0.83}$Fe$_{1.53}$Se$_2$, identifying key electronic excitations and their orbital origins, with theoretical modeling supporting moderate electron correlations.

Findings

Identified a sharp 1 eV excitation with momentum dependence.

Observed broad interband transitions at 3-7 eV independent of momentum.

Theoretical calculations indicate the 1 eV feature arises from correlated Fe 3d electrons with moderate U_eff.

Abstract

We report an Fe $K$-edge resonant inelastic X-ray scattering (RIXS) study of K$_{0.83}$Fe$_{1.53}$Se$_2$. This material is an insulator, unlike many parent compounds of iron-based superconductors. We found a sharp excitation around 1 eV, which is resonantly enhanced when the incident photon energy is tuned near the pre-edge region of the absorption spectrum. The spectral weight and line shape of this excitation exhibit clear momentum dependence. In addition, we observe momentum-independent broad interband transitions at higher excitation energy of 3-7 eV. Calculations based on a 70 band $dp$ orbital model, using a moderate $U_{\rm eff}\approx 2.5$ eV, indicate that the $\sim$1 eV feature originates from the correlated Fe 3$d$ electrons, with a dominant $d_{xz}$ and $d_{yz}$ orbital character. We find that a moderate $U_{\rm eff}$ yields a satisfying agreement with the experimental spectra, suggesting that the electron correlations in the insulating and metallic iron based superconductors are comparable.