Superconducting properties of MBE-grown 3<i>R</i>-Ta_1+<i>x</i>Se₂ epitaxial thin films

2D materials research is one of the hot topics in condensed-matter science, but most studies are performed on nanometer-thick crystals fabricated by mechanical exfoliation. On the other hand, researches based on MBE-grown samples are very much limited in particular for transport studies presumably due to difficulties in making high quality thin films. We have recently established a versatile route to layer-by-layer epitaxial growth of a wide variety of 2D materials and their heterostructures on insulating sapphire substrates by MBE [1,2], opening a door for exploration of emergent transport phenomena even based on hardly-cleavable and/or thermodynamically-metastable compounds. In this presentation, we will report MBE growth of thermodynamically-metastable 3R-Ta_1+xSe₂ epitaxial thin films and their superconducting properties, which turned out to be very much different from those of thermodynamically-stable 2H-TaSe₂ in terms of T_c and superconducting anisotropy. [1] M. Nakano et al., Nano Lett. 17, 5595 (2017). [2] Y. Kashiwabara et al., Adv. Funct. Mater. 2019, 1900354 (2019).