Pal Banabir, Cao Yanwei, Liu Xiaoran, Wen Fangdi, Kareev M, N'Diaye A T, Shafer P, Arenholz E, Chakhalian J
Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, 08854, USA.
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, Zhejiang, 315201, China.
Sci Rep. 2019 Feb 13;9(1):1896. doi: 10.1038/s41598-018-37248-5.
Generally, lattice distortions play a key role in determining the electronic ground states of materials. Although it is well known that trigonal distortions are generic to most two dimensional transition metal dichalcogenides, the impact of this structural distortion on the electronic structure and topological properties has not been understood conclusively. Here, by using a combination of polarization dependent X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) and atomic multiplet cluster calculations, we have investigated the electronic structure of titanium dichalcogenides TiX (X = S, Se, Te), where the magnitude of the trigonal distortion increase monotonically from S to Se and Te. Our results reveal the presence of an anomalously large crystal field splitting. This unusual kind of crystal field splitting is likely responsible for the unconventional electronic structure of TiX compounds and ultimately controls the degree of the electronic phase protection. Our findings also indicate the drawback of the distorted crystal field picture in explaining the observed electronic ground state and emphasize the key importance of trigonal symmetry, metal-ligand hybridization and electron-electron correlations in defining the electronic structures at the Fermi energy.
一般来说，晶格畸变在决定材料的电子基态方面起着关键作用。尽管众所周知，三角畸变在大多数二维过渡金属二硫属化物中很常见，但这种结构畸变对电子结构和拓扑性质的影响尚未得到确凿的理解。在这里，通过结合偏振相关的X射线吸收光谱（XAS）、X射线光电子能谱（XPS）和原子多重态簇计算，我们研究了二硫属化钛TiX（X = S、Se、Te）的电子结构，其中三角畸变的程度从S到Se和Te单调增加。我们的结果揭示了存在异常大的晶体场分裂。这种不寻常的晶体场分裂可能是TiX化合物非常规电子结构的原因，并最终控制电子相保护的程度。我们的发现还表明，畸变晶体场图像在解释观察到的电子基态方面存在缺陷，并强调了三角对称性、金属-配体杂化和电子-电子相关性在定义费米能级处的电子结构中的关键重要性。
