Bandgap opening in MoTe2 thin flakes induced by surface oxidation
Bandgap opening in MoTe2 thin flakes induced by surface oxidation
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DOI：
10.1007/s11467-020-0952-x
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发表时间：
2020-03-05
影响因子：
7.5
通讯作者：
Zhang, Liyuan
中科院分区：
文献类型：
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作者：
Gan, Yuan;Liang, Jiyuan;Zhang, Liyuan
近年来，层状过渡金属二硫化物1T′-MoTe2由于其超导和非平凡的拓扑性质而引起了相当大的兴趣。本文采用电输运、扫描隧道显微镜（STM）测量和能带结构计算等方法对1T’-MoTe2单晶和剥离薄片进行了系统的研究。对于大块样品，它在低温下表现出较大的磁阻（MR）和rho xx中的舒布尼科夫-德哈斯振荡和rho xy中的一系列霍尔高原。同时，深入研究了MoTe2薄膜的厚度依赖性。对于没有封装的样品，通过减小厚度可以观察到从固有金属状态到绝缘状态的明显转变。在这种薄膜中，我们还观察到抑制MR和弱反定位（WAL）效应。我们将这些影响归因于外在表面化学反应引起的紊乱，这与密度泛函理论（DFT）计算和原位STM结果一致。与没有封装保护的样品相比，我们发现具有六方氮化硼（h-BN）薄膜保护的样品具有有趣的超导转变。我们的结果表明，金属或超导行为是其固有状态，绝缘行为可能是由少数层1T'-MoTe2薄片的表面氧化引起的。
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 rho xx and a series of Hall plateaus in rho 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.