Role of electron-phonon coupling in excitonic insulator candidate Ta2NiSe5
Role of electron-phonon coupling in excitonic insulator candidate Ta2NiSe5
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DOI：
10.1103/physrevresearch.5.043089
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发表时间：
2023-10-26
影响因子：
4.2
通讯作者：
He, Yu
中科院分区：
文献类型：
--
作者：
Chen, Cheng;Chen, Xiang;He, Yu
电子-空穴束缚对或激子是半导体中常见的激发。当电子-空穴库仑吸引的能量超过带隙时，它们可以自发地形成并凝聚成一个新的绝缘基态--所谓的激子绝缘体。在电子-声子耦合的存在下，周期性的晶格畸变经常伴随发生。然而，电子-声子耦合本身也可以诱导类似的结构转变，因此阻碍了体激子绝缘体（例如，该不稳定性是相变的驱动力）。使用高分辨率同步辐射X射线衍射和角分辨光电子能谱，我们确定了领先的激子绝缘体候选人Ta 2NiSe 5中的关键电子-声子耦合效应。这些包括一个广泛的单向晶格波动和电子赝隙在正常状态下，以及负的电子可压缩性的电荷掺杂的对称性破缺状态。结合第一性原理和模型计算，我们使用正常态的电子光谱，以定量地确定在最小晶格模型中的电子-声子相互作用顶点g和带间库仑相互作用V，该解决方案捕获的实验观察。此外，我们展示了如何库仑和电子-声子耦合效应可以明确分离的基础上的解决方案，以量化的微观模型。最后，我们讨论了如何使低维强晶格涨落涉及到独特的电子-声子相互作用的影响超出了教科书玻恩-奥本海默近似。
Electron-hole bound pairs, or excitons, are common excitations in semiconductors. They can spontaneously form and condense into a new insulating ground state-the so-called excitonic insulator-when the energy of electron-hole Coulomb attraction exceeds the band gap. In the presence of electron-phonon coupling, a periodic lattice distortion often concomitantly occurs. However, a similar structural transition can also be induced by electron-phonon coupling itself, therefore hindering the clean identification of bulk excitonic insulators (e.g., which instability is the driving force of the phase transition). Using high-resolution synchrotron x-ray diffraction and angle-resolved photoemission spectroscopy, we identify key electron-phonon coupling effects in a leading excitonic insulator candidate Ta2NiSe5. These include an extensive unidirectional lattice fluctuation and an electronic pseudogap in the normal state, as well as a negative electronic compressibility in the charge-doped broken-symmetry state. In combination with first principles and model calculations, we use the normal state electronic spectra to quantitatively determine the electron-phonon interaction vertex g and interband Coulomb interaction V in the minimal lattice model, the solution to which captures the experimental observations. Moreover, we show how the Coulomb and electron-phonon coupling effects can be unambiguously separated based on the solution to quantified microscopic models. Finally, we discuss how the strong lattice fluctuations enabled by low dimensionality relate to the unique electron-phonon interaction effects beyond the textbook Born-Oppenheimer approximation..