Structural and Electronic Phases of 2D Transition Metal Dichalcogenides

Layered transition metal dichalcogenides (TMDs) of chemical composition MX₂ (M = transition metal; X = S, Se, or Te) represent a broad family of materials with diverse electronic properties, including metals, insulators, as well as more complex states such as the charge-density-wave (CDW) and superconducting phases. More recently, the possibility of realizing single- and few-layer TMDs has brought the two-dimensional (2D) forms of these materials into the spotlight of prospective application in electronics, optoelectronics and beyond [1]. In my talk, I will review the “periodic table” of TMDs attempting to reveal systematic trends and develop chemical intuition across this family of 2D materials. Using a Wannier function approach, I will address the relevance of the crystal and ligand fields in determining the relative stability of 1T and 1H polymorphs as a function of the filling of the d-shell in 2D TMDs [2]. Then, I will present a unified picture of lattice instabilities in metallic TMDs that describes both the CDW phases and the strong-coupling scenario resulting in the formation of metal-metal bonds (as e.g. in the dimerized 1T’ phases) [3]. In the rest of my talk, I will focus on topological and magnetic phases of TMDs. The 1T’-phase of Mo and W TMDs that have recently been shown to host the topologically non-trivial quantum spin Hall (QSH) insulator phase. The robustness of the QSH phase as well as the topological edge states [4] and interface states at the well-ordered 1T’-1H lateral heterojunctions will be discussed in conjunction with recent experiments on 1T’-WSe₂ [5]. I will also cover our recent discovery of magnetic ordering and magnetoresistive switching in metallic few-layer and insulating single-layer PtSe₂ [6,7].

1. S. Manzeli, D. Ovchinnikov, D. Pasquier, O. V. Yazyev and A. Kis, Nature Rev. Mater. 2, 17033 (2017).
2. D. Pasquier and O. V. Yazyev, 2D Materials 6, 025015 (2019).
3. D. Pasquier and O. V. Yazyev, Phys. Rev. B 100, 201103(R) (2019).
4. A. Pulkin and O. V. Yazyev, J. Phys. Chem. Lett. 11, 6964 (2020).
5. M. M. Ugeda et al., Nature Commun. 9, 3401 (2018).
6. A. Avsar et al., Nature Nanotechnol. 14, 674 (2019).
7. A. Avsar et al., Nature Commun. 11, 4806 (2020).