The transition metal chalcogenide Ta2NiSe5 undergoes a second-order phase transition at Tc=328 K involving a small lattice distortion. Below Tc, a band gap at the center of its Brillouin zone increases up to about 0.35 eV. In this work, we study the electronic structure of Ta2NiSe5 in its low-temperature semiconducting phase, using resonant inelastic x-ray scattering (RIXS) at the Ni L3-edge. In addition to a weak fluorescence response, we observe a collection of intense Raman-like peaks that we attribute to electron-hole excitations. Using density functional theory calculations of its electronic band structure, we identify the main Raman-like peaks as interband transitions between valence and conduction bands. By performing angle-dependent RIXS measurements, we uncover the dispersion of these electron-hole excitations that allows us to extract the low-energy boundary of the electron-hole continuum. From the dispersion of the valence band measured by angle-resolved photoemission spectroscopy, we derive the effective mass of the lowest unoccupied conduction band.
@article{arxiv.2008.02575,
title = {Mapping the unoccupied state dispersions in Ta$_2$NiSe$_5$ with resonant inelastic x-ray scattering},
author = {C. Monney and M. Herzog and A. Pulkkinen and Y. Huang and J. Pelliciari and P. Olalde-Velasco and N. Katayama and M. Nohara and H. Takagi and T. Schmitt and T. Mizokawa},
journal= {arXiv preprint arXiv:2008.02575},
year = {2020}
}