| AVS 66th International Symposium & Exhibition | |
| 2D Materials | Tuesday Sessions |
| Session 2D+EM+MI+MN+NS+QS-TuM |
| Session: | Novel Quantum Phenomena |
| Presenter: | Phil King, University of St Andrews, UK |
| Correspondent: | Click to Email |
Control over materials thickness down to the single-atom scale has emerged as a powerful tuning parameter for manipulating not only the single-particle band structures of solids, but increasingly also their interacting electronic states and phases. A particularly attractive materials system in which to explore this is the transition-metal dichalcogenides, both because of their naturally-layered van der Waals structures as well as the wide variety of materials properties which they are known to host. Yet, how their interacting electronic states and phases evolve when thinned to the single-layer limit remains a key open question in many such systems. Here, we use angle-resolved photoemission to investigate the electronic structure and charge density wave (CDW) phases of monolayer TiSe2, TiTe2, and VSe2. Three-dimensionality is a core feature of the electronic structure of all of these parent compounds, but we show how their CDW phases not only persist, but are strengthened, in the monolayer limit. In TiSe2, we observe an orbital-selective CDW, necessarily without a kz-selectivity in band hybridisation that is of key importance for the bulk instability,1 while TiTe2 is driven into a charge-ordered phase in the monolayer which is not stable in the bulk at all. In VSe2, we show how the monolayer hosts a much stronger-coupling CDW instability than the bulk, which in turn drives a metal-insulator transition, removing a competing instability to ferromagnetism.2 Together, these studies point to the delicate balance that can be realized between competing interacting states and phases in monolayer transition-metal dichalcogenides.
This work was performed in close collaboration with M.D. Watson, A. Rajan, J. Feng, D. Biswas, and colleagues from the Universities of St Andrews, Oxford, Keil, Diamond, Elettra, and SOLEIL.
1Watson et al., Phys. Rev. Lett. 122 (2019) 076404.
2Feng et al., Nano Lett. 18 (2018) 4493.