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Uniaxial negative thermal expansion and band renormalization in monolayer T_d-MoTe_2 at low temperature

机译：低温下单层T_d-MoTe_2的单轴负热膨胀和能带归一化

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摘要

The temperature-induced structure variation and its effect on physical properties is pivotal in material preparation for devices application. Motivated by surface scanning tunnel microscope (STM) measurement of T_d-MoTe_2 single crystal at low temperature, temperature dependent electronic structure, lattice dynamics, and topological properties are explored to understand the microscopic origin of the observed anisotropic negative thermal expansion and abnormal STM images below 70 K. Remarkably, we find that the nonequivalent Te atoms in T_d-MoTe_2 have qualitatively different contributions to both phonon spectra and electronic structures. The in-plane longitudinal acoustic mode and the Te_((2)) atoms are found to play an important role in uniaxial negative thermal expansion and the temperature dependent electronic phase transition, respectively. Interestingly, under the scalar relativistic approximation, a band renormalization occurs, accompanied by a Dirac phase transition from type Ⅱ to type Ⅰ, upon cooling below 70 K. Introducing spin-orbit coupling induces a temperature dependent semimetal-semiconductor transition. Our results explain the experimental phenomena very well: abnormal surface STM image below 70 K does not originate from the displacement of the Te atoms but the band renormalization owing to strong electron-lattice coupling.
机译：温度引起的结构变化及其对物理性能的影响在器件应用的材料制备中至关重要。通过表面扫描隧道显微镜（STM）在低温下测量T_d-MoTe_2单晶的动机，与温度相关的电子结构，晶格动力学和拓扑性质进行了探索，以了解观察到的各向异性负热膨胀和下面异常STM图像的微观起源。 70K。值得注意的是，我们发现T_d-MoTe_2中非等价的Te原子对声子光谱和电子结构的贡献在质量上都不同。发现面内纵向声模和Te _（（2））原子分别在单轴负热膨胀和与温度有关的电子相变中起重要作用。有趣的是，在标量相对论近似下，当冷却至70 K以下时，会发生能带重整化，并伴有Dirac从Ⅱ型到Ⅰ型的相变。自旋轨道耦合的引入引起温度依赖性半金属-半导体的转变。我们的结果很好地说明了实验现象：低于70 K的异常表面STM图像并非源自Te原子的位移，而是由于强的电子-晶格耦合而使能带重新归一化。

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  • 来源
    《Physical review》 |2020年第10期|104305.1-104305.6|共6页
  • 作者

    Yu Ge; Zhenyu Ding; Wenjie Meng; Jihao Wang; Yubin Hou; Gang Wu; Qingyou Lu; Xiaoping Yang;

  • 作者单位

    Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions High Magnetic Field Laboratory Chinese Academy of Sciences Hefei 230031 China Science Island Branch of Graduate School University of Science and Technology of China Hefei 230026 China;

    Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions High Magnetic Field Laboratory Chinese Academy of Sciences Hefei 230031 China;

    Institute of High Performance Computing 1 Fusionopolis Way 16-16 Connexis Singapore 138632 Singapore;

    Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions High Magnetic Field Laboratory Chinese Academy of Sciences Hefei 230031 China Hefei National Laboratory for Physical Sciences at the Microscale University of Science and Technology of China Hefei 230026 China Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 China Hefei Science Center Chinese Academy of Sciences Hefei 230031 China;

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