Electronic structure of 3d transition-matal dichalcogenide thin films grown by molecular-beam epitaxy

There has been increasing interest in atomically-thin transition-metal dichalcogenides (TMDs) hosting intriguing properties absent in their bulk form. For example, in 4d and 5d transition-metal TMDs such as MoS₂, WSe₂, and NbSe₂, valley degree of freedom plays an important role on novel two-dimensional properties. 3d TMDs, on the other hand, are expected to exhibit more varieties of phenomena involving excitonic physics, charge density wave, and magnetism, due to stronger electron-electron, electron-lattice and exchange interactions. Recently, emergent ferromagnetism in monolayer VSe₂ was reported, although the situation is still controversial. To unambiguously characterize physical properties of atomically thin TMDs and further understand the origin of the emergent two-dimensional phenomena, the direct observation of electronic structures is crucial. We have fabricated atomically thin films of 3d TMDs by molecular-beam epitaxy with our growth recipe [1] and clarified electronic structures by angle-resolved photoemission spectroscopy (ARPES). In this presentation, we will discuss the physical properties appearing in two-dimensional 3d TMDs by comparison with the ARPES results and band calculations. [1] M. Nakano, et al., Nano Lett. 17, 5595 (2017).