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首页> 外文期刊>Physical review >Collective modes in excitonic insulators: Effects of electron-phonon coupling and signatures in the optical response
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Collective modes in excitonic insulators: Effects of electron-phonon coupling and signatures in the optical response

机译：激发器绝缘子中的集体模式：电子 - 声子耦合和签名在光学响应中的影响

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摘要

We consider a two-band spinless model describing an excitonic insulator (EI) on the two-dimensional square lattice with anisotropic hopping parameters and electron-phonon (el-ph) coupling, inspired by the HI candidate Ta_2NiSe_5. We systematically study the nature of the collective excitations in the ordered phase which originates from the interband Coulomb interaction and the el-ph coupling. When the ordered phase is stabilized only by the Coulomb interaction (pure EI phase), its collective response exhibits a massless phase mode in addition to the amplitude mode. We show that in the BEC regime, the signal of the amplitude mode becomes less prominent and that the anisotropy in the phase-mode velocities is reduced. Through coupling to the lattice, the phase mode acquires a mass and the signal of the amplitude mode becomes less prominent. Importantly, the character of the softening mode at the boundary between the normal semiconductor phase and the ordered phase depends on the parameters. In particular, we point out that even for el-ph coupling smaller than the Coulomb interaction, the mode that softens to zero at the boundary can have a phonon character. We also discuss how the collective modes can be observed in the optical conductivity. Furthermore, we study the effects of nonlocal interactions on the collective modes and show the possibility of realizing a coexistence of an in-gap mode and an above-gap mode split off from the single-amplitude mode in the system with local interactions only.
机译：我们考虑一个双频无纺布模型，其在二维方形格子上描述了具有各向异性跳跃参数和电子 - 声子（EL-PH）耦合的二维方形格子（EI），受到HI候选Ta_2nise_5的启发。我们系统地研究了所订购的相位中集体激励的性质，该阶段源自间带间库仑相互作用和EL-pH耦合。当仅通过库仑相互作用（纯EI阶段）稳定有序相时，其集体响应除了幅度模式之外还表现出无麻的相位模式。我们表明，在BEC制度中，幅度模式的信号变得不太突出，并且减少了相位模式速度中的各向异性。通过耦合到晶格，相位模式获取质量并且幅度模式的信号变得不那么突出。重要的是，在正常半导体阶段和有序相之间的边界处的软化模式的特征取决于参数。特别地，我们指出即使对于小于库仑相互作用的EL-pH耦合，在边界处软化为零的模式也可以具有声子字符。我们还讨论如何在光导中观察到集体模式。此外，我们研究了非局部相互作用对集体模式的影响，并示出了实现内隙模式的共存和上面间隙模式从系统中的单个幅度模式分开的可能性，仅具有本地交互。

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  • 来源
    《Physical review》 |2020年第19期|195118.1-195118.17|共17页
  • 作者

    Yuta Murakami; Denis Golez; Tatsuya Kaneko; Akihisa Koga; Andrew J. Millis; Philipp Werner;

  • 作者单位

    Department of Physics Tokyo Institute of Technology Meguro Tokyo 152-8551 Japan;

    Center for Computational Quantum Physics Flatiron Institute New York New York 10010 USA;

    Department of Physics Columbia University New York New York 10027 USA;

    Department of Physics Tokyo Institute of Technology Meguro Tokyo 152-8551 Japan;

    Center for Computational Quantum Physics Flatiron Institute New York New York 10010 USA Department of Physics Columbia University New York New York 10027 USA;

    Department of Physics University of Fribourg 1700 Fribourg Switzerland;

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