Spin–Orbit Coupling-Determined Topological Phase: Topological Insulator and Quadratic Dirac Semimetals

• Published in: The journal of physical chemistry letters Vol. 11; no. 24; pp. 10340 - 10347
• Main Authors: Tian, Lu, Liu, Ying, Meng, Weizhen, Zhang, Xiaoming, Dai, Xuefang, Liu, Guodong
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.12.2020
• Subjects: Physical Insights into Materials and Molecular Properties
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.0c03103

Our work reveals a class of three-dimensional materials whose main features are dominated by d-orbital states. Their unique properties are derived from the low-energy states t2g. Without spin–orbital coupling (SOC), we find a triple degenerate point with a quadratic dispersion, demonstrated by an effective Hamiltonian. When SOC is included, the sign of SOC could determine the topological phases of materials: a negative SOC contributes a Dirac semimetal phase with a quadratic energy dispersion, whereas a positive SOC leads to a strong topological insulator phase. There exist clear surface states for the corresponding topological phases. Very interestingly, by application of a triaxial strain, the sequence of bands can be exchanged, as do the topological phases. In particular, there exists a 6-fold degenerate point under a critical strain. Furthermore, we use a uniaxial compressive/tensile strain, changing the quadratic Dirac point into a linear Dirac/strong topological insulator phase.