Thickness-Tunable Synthesis of Ultrathin Type-II Dirac Semimetal PtTe₂ Single Crystals and Their Thickness-Dependent Electronic Properties

Abstract

The recent discovery of topological semimetals has stimulated extensive research interest due to their unique electronic properties and novel transport properties related to a chiral anomaly. However, the studies to date are largely limited to bulk crystals and exfoliated flakes. Here, we report the controllable synthesis of ultrathin two-dimensional (2D) platinum telluride (PtTe) nanosheets with tunable thickness and investigate the thickness-dependent electronic properties. We show that PtTe nanosheets can be readily grown, using a chemical vapor deposition approach, with a hexagonal or triangular geometry and a lateral dimension of up to 80 μm, and the thickness of the nanosheets can be systematically tailored from over 20 to 1.8 nm by reducing the growth temperature or increasing the flow rate of the carrier gas. X-ray-diffraction, transmission-electron microscopy, and electron-diffraction studies confirm that the resulting 2D nanosheets are high-quality single crystals. Raman spectroscopic studies show characteristics E and A vibration modes at ∼109 and ∼155 cm, with a systematic red shift with increasing nanosheet thickness. Electrical transport studies show the 2D PtTe nanosheets display an excellent conductivity up to 2.5 × 10 S m and show strong thickness-tunable electrical properties, with both the conductivity and its temperature dependence varying considerably with the thickness. Moreover, 2D PtTe nanosheets show an extraordinary breakdown current density up to 5.7 × 10 A/cm, the highest breakdown current density achieved in 2D metallic transition-metal dichalcogenides to date.

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

“…The conductivity of the PtTe 2 thin films (3–20 nm) at room temperature is in the range of 0.2–3 × 10 6 S m −1 , as shown in Figure a, which is consistent with that of single‐crystal PtTe 2 flakes. [ 35 ] This again indicates the high quality of these thin films. The increase of conductivity upon decreasing temperature signifies their metallic behavior.…”

“…Such a trend is in agreement with the results of PtTe 2 crystals grown by the chemical vapor deposition (CVD) method. [ 35 ] The 0.5–4 nm Pt thin films become 3–20 nm PtTe 2 after transformation, which are measured by atomic force microscopy (AFM). Their root‐means‐square (RMS) roughnesses are all less than 0.7 nm in a 5 × 5 µm 2 area (Figure S1b, Supporting Information).…”

Metal-chalcogen bond-length induced electronic phase transition from semiconductor to topological semimetal in ZrX2 ( X=Se and Te)

“…Transition metal dichalcogenides (TMDCs) [1][2][3] are gaining a great deal of research interests, especially, from the past few decades due to their potential applications in the spintronics [4][5][6][7][8] and as well in the optoelectronics [9][10][11][12][13] because of their wide range of electronic properties starting from the metallic [14][15][16], to the semimetallic [17][18][19][20], to the semiconducting [21][22][23][24], and to the Mott-insulators [25][26][27], obtained mainly by the band engineering [28][29][30]. In addition, the diversity of electronic properties of TMDCs includes the charge density wave (CDW) [31,32], the magnetism [33][34][35], and the superconductivity [36][37][38].…”

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

“…Growth of PtTe2 thin films with thickness down to a few nanometers has been reported by chemical vapor deposition (CVD) recently [20][21][22]. However, so far there is no report of thinner (sub-nanometer) films and the experimental electronic structure of PtTe2 films still remains to be explored.…”