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

Abstract

PtTe 2 and PtSe 2 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 PtSe 2 , so far the evolution of electronic structure of atomically thin PtTe 2 films still remains unexplored. Here we report a systematic angleresolved photoemission spectroscopy (ARPES) study of the electronic structure of high quality PtTe 2 films grown by molecular beam epitaxy with thickness from 2 ML to 6 ML. ARPES measurements show that PtTe 2 films still remain metallic even down to 2 ML thickness, which is in sharp contrast to the semiconducting property of few layer PtSe 2 film. 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 PtTe 2 crystal, suggesting that similar hidden spin is also expected in few monolayer PtTe 2 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.

High Spin Hall Conductivity in Large‐Area Type‐II Dirac Semimetal PtTe2

“…The interface between PtTe 2 and Py might play a role through the Rashba–Edelstein effect. [ 28 ] However, in that case, a significant field‐like torque [ 47 ] and a negative ξ SOT would appear, [ 25 ] which is in contradiction with our observation. It was reported in Bi x Se 1‐x nanocrystalline thin films that the enhanced ξ SOT can be ascribed to the quantum confinement effect from tiny crystal grains (≈6 nm).…”

“…Moreover, the helical spin textures at the Fermi level was observed in few‐layer PtTe 2 and ascribed to the local Rashba effect. [ 28 ] Motivated by these intriguing properties, the potential of PtTe 2 in SOT device applications calls for further investigation.…”

Imaging and identification of point defects in PtTe2

“…Nevertheless, the energy level of the VBM exceeds that of the CBM, even using the GGA-1/2 technique, leading to an overlap of bands; hence, a semimetal-to-semiconductor transition occurs in this material due to quantum confinement. This is consistent with angle-resolved photoemission studies that have shown BL PtTe 2 to be metallic 34 . The band overlap increases even further for bulk PtTe 2 as shown in Fig.…”

“…Careful classification and characterization of these defects can allow us to understand their impact on the electronic properties of the intrinsic materials and assess their significance with a view to potential applications. The crystal structure of PtTe 2 has been characterized by transmission electron microscopy (TEM) in several experimental studies 19,21,34 . Although TEM can routinely resolve the atomic structure of materials, it cannot provide easy access to the electronic band structure around the Fermi level of individual point defects.…”

Two-dimensional materials: new opportunities for electronics, photonics and optoelectronics

“…However, the evolution of electronic structure of atomically thin PtTe 2 films still remains elusive. Zhou's group [11] from Tsinghua University has revealed that the PtTe 2 film evolves from a 2D metallic at 2 ML to a 3D Dirac semimetal at 4-6 ML thickness based on the angle-resolved photoemission spectroscopy (ARPES). The helical spin texture induced by the local Rashba effect in bulk PtTe 2 was reported in the meanwhile.…”