RESEARCH ARTICLE

Front. Phys. 15(3), 33602 (2020) 

Bandgap opening in MoTe₂ thin flakes induced by surface oxidation

Yuan Gan^1,2, Jiyuan Liang², Chang-woo Cho², Si Li^3,4, Yanping Guo², Xiaoming Ma^2,5, Xuefeng Wu², Jinsheng Wen¹, Xu Du⁶, Mingquan He⁷, Chang Liu², Shengyuan A. Yang⁴, Kedong Wang², Liyuan Zhang^2,*

¹National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
²Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China
³School of Physics and Electronics, Hunan Normal University, Changsha 410081, China
⁴Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
⁵Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
⁶Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794, USA
⁷Chongqing Key Laboratory of Soft Condensed Matter Physics and Smart Materials, College of Physics, Chongqing University, Chongqing 401331, China

Recently, the layered transition metal dichalcogenide 1T′-MoTe₂ has generated considerable interest due to their superconducting and non-trivial topological properties. Here, we present a systematic study on 1T′-MoTe₂ single-crystal and exfoliated thin-flakes by means of electrical transport, scanning tunnelling microscope (STM) measurements and band structure calculations. For a bulk sample, it exhibits large magneto-resistance (MR) and Shubnikov–de Hass oscillations in ρ_xx and a series of Hall plateaus in ρ_xy at low temperatures. Meanwhile, the MoTe₂ thin films were intensively investigated with thickness dependence. For samples, without encapsulation, an apparent transition from the intrinsic metallic to insulating state is observed by reducing thickness. In such thin films, we also observed a suppression of the MR and weak anti-localization (WAL) effects. We attributed these effects to disorders originated from the extrinsic surface chemical reaction, which is consistent with the density functional theory (DFT) calculations and in-situ STM results. In contrast to samples without encapsulated protection, we discovered an interesting superconducting transition for those samples with hexagonal Boron Nitride (h-BN) film protection. Our results indicate that the metallic or superconducting behavior is its intrinsic state, and the insulating behavior is likely caused by surface oxidation in few layer 1T′-MoTe₂ flakes.

全文下载：

http://journal.hep.com.cn/fop/EN/10.1007/s11467-020-0952-x