Momentum-Dependent Charge Transfer Excitations in Sr2CuO2Cl2 - Angle Resolved Electron Energy Loss Spectroscopy

TL;DR

This study uses angle-resolved electron energy loss spectroscopy to investigate charge transfer excitations in Sr2CuO2Cl2, revealing anisotropic exciton behavior and energy dispersions in the cuprate material.

Contribution

It provides new insights into the momentum-dependent charge transfer excitations and excitonic transitions in Sr2CuO2Cl2 using a novel spectroscopic approach.

Findings

Optically allowed and forbidden transitions are strongly anisotropic.

Large energy dispersion (~1.5 eV) observed along [110].

Higher energy transitions (~4.5 eV) are only along [100].

Abstract

Electron-hole pair excitations in the insulating cuprates $Sr_2CuO_2Cl_2$ were investigated by angle-resolved electron energy loss spectroscopy. The optically allowed and optically forbidden transitions were observed to be strongly anisotropic in $Cu-O_2$ plane. The former show a large energy dispersion $\sim 1.5$eV along [110], and the latter appear at a higher energy position ($\sim 4.5$eV) only along [100], but not along [110]. We interpret these results as transitions involving excitons. A small exciton model is examined to explain both the observed features.