Strong Electron-Phonon Coupling in the Excitonic Insulator Ta2NiSe5.
Strong Electron-Phonon Coupling in the Excitonic Insulator Ta2NiSe5.
复制标题
激子绝缘体 Ta2NiSe5 中的强电子声子耦合。
作者：
Jian‐Min Yan;R. Xiao;Xuan Luo;H. Lv;Ranran Zhang;Yan Sun;P. Tong;Wenjian Lu;W. Song;Xuebin Zhu;Yuping Sun
激子绝缘态（EI）是凝聚态物理中一种由屏蔽电子-空穴相互作用驱动的奇异关联电子相。Ta_2NiSe_5是一种激子绝缘体，其临界温度（TC）为328 K。在目前的研究中，温度依赖的拉曼光谱被用来调查的声子振动在Ta 2 NiSe 5。观察到：（1）在TC附近观察到一个异常的蓝移，这是由单斜晶向正交晶的结构相变引起的;（2）在147和235 cm-1处观察到一个模式的分裂和两个新的拉曼模式，并形成一个EI态。借助第一性原理计算和变温X射线衍射（XRD）实验，发现在低于TC时TaSe 6八面体被“冻结”，NiSe 4四面体发生了很大的畸变.因此，NiSe 4四面体的畸变在Ta 2NiSe 5中的强电子-声子耦合（EPC）中起着重要作用，而强EPC与电子-空穴相互作用相耦合，打开了能隙，形成了Ta 2NiSe 5中的EI态.
An excitonic insulating (EI) state is a fantastic correlated electron phase in condensed matter physics, driven by screened electron-hole interaction. Ta2NiSe5 is an excitonic insulator with a critical temperature ( TC) of 328 K. In the current study, temperature-dependent Raman spectroscopy is used to investigate the phonon vibrations in Ta2NiSe5. The following observations were made: (1) an abnormal blue shift around TC is observed, which originates from the monoclinic to orthorhombic structural phase transition; (2) the splitting of a mode and two new Raman modes at 147 and 235 cm-1 have been observed with the formation of an EI state. With the help of first-principles calculations and temperature-dependent X-ray diffraction (XRD) experiments, it is found that the TaSe6 octahedra are "frozen" and the NiSe4 tetrahedra are greatly distorted below TC. Thus, it seems that the distortion of NiSe4 tetrahedra plays an important role in the strong electron-phonon coupling (EPC) in Ta2NiSe5, while the strong EPC, coupled with electron-hole interaction, opens the energy gap to form the EI state in Ta2NiSe5.