Momentum patterns of NiTe₂ by two-photon photoemission

Cheng-Tien Chiang^1,2,3*, Mukesh Singh^1,4, Yu-Jhen Chuang^1,2, Chia-Nung Kuo⁵, Chin Shan Lue^5,6

¹Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
²Department of Physics, National Taiwan University, Taipei, Taiwan
³Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
⁴Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia, USA
⁵Department of Physics, National Cheng Kung University, Tainan, Taiwan
⁶Taiwan Consortium of Emergent Crystalline Materials, National Science and Technology Council, Taipei, Taiwan

* Presenter:Cheng-Tien Chiang, email:ctchiang@as.edu.tw

The metallic transition metal dichalcogenide NiTe₂ has attracted recent attention due to its possible relevance to strong electron correlation and electronic topology [1]. Despite that it has been intensively studied by various experimental and theoretical methods, the momentum patterns of the NiTe₂ valence electronic bands have been rarely revealed in the angle-resolved photoelectron spectroscopy [1,2] and scanning tunneling spectroscopy [3] experiments so far. As the only modern tool to resolve the energy-momentum dispersion relation of the unoccupied electronic structure of solids, two-photon photoemission spectroscopy (2PPE) has been applied to transition metal dichalcogenides other than NiTe₂ previously [4]. In this invited talk, our ongoing development of 2PPE using the time-of-flight momentum microscopy [5] and its application to NiTe₂ will be shown. Specifically we demonstrate that the spin-orbit split Te 5p_x,y valence bands can be clearly identified by their momentum patterns in 2PPE for the first time worldwide, and a size of splitting around 0.5 eV can be estimated [6].

[1] N. Blatt et al., Phys. Rev. B 111, 245157 (2025).
[2] M. Nurmamat et al., Phys. Rev. B 104, 155133 (2021).
[3] M. Ren et al., Phys. Rev. B 108, 235408 (2023).
[4] D. A. Racke et al., Phys. Rev. B 93, 085309 (2016); M. Wiesenmayer et al., ibid. 82, 035422 (2010); A. Tanaka et al., ibid. 67, 113315 (2003); C. Jiao et al., Front. Phys. 19, 33207 (2024); C. Xu et al., ACS Nano 18, 1931 (2024); P. Hein et al., J. Phys. Condens. Matter 32, 345503 (2020).
[5] G. Schönhense and H.-J. Elmers, J. Vac. Sci. Technol. A 40, 020802 (2022).
[6] N. H. Lam et al., ACS Nano 16, 11227 (2022).

Keywords: two-photon photoemission, transition metal dichalcogenide, momentum microscopy, spin-orbit coupling, band structure