Crossover from 2D metal to 3D Dirac semimetal in metallic PtTe₂ films with local Rashba effect

PtTe₂ and PtSe₂ with trigonal structure have attracted extensive research interests since the discovery of type-II Dirac fermions in the bulk crystals. The evolution of the electronic structure from bulk 3D topological semimetal to 2D atomic thin films is an important scientific question. While a transition from 3D type-II Dirac semimetal in the bulk to 2D semiconductor in monolayer (ML) film has been reported for PtSe₂, so far the evolution of electronic structure of atomically thin PtTe₂ films still remains unexplored. Here we report a systematic angle-resolved photoemission spectroscopy (ARPES) study of the electronic structure of high quality PtTe₂ films grown by molecular beam epitaxy with thickness from 2 ML to 6 ML. ARPES measurements show that PtTe₂ films still remain metallic even down to 2 ML thickness, which is in sharp contrast to the semiconducting property of few layer PtSe₂ films. Moreover, a transition from 2D metal to 3D type-II Dirac semimetal occurs at film thickness of 4-6 ML. In addition, Spin-ARPES measurements reveal helical spin textures induced by local Rashba effect in the bulk PtTe₂ crystal, suggesting that similar hidden spin is also expected in few monolayer PtTe₂ films. Our work reveals the transition from 2D metal to 3D topological semimetal and provides new opportunities for investigating metallic 2D films with local Rashba effect.