近日，上海交通大学物理与天文学院的陈鹏及其研究团队取得一项新进展。经过不懈努力，他们成功观察到原子薄半金属中可能的激子电荷密度波和金属绝缘体转变。相关研究成果已于2024年1月23日在国际知名学术期刊《自然—物理学》上发表。
该研究团队研究了低维HfTe2中的凝聚相。通过角度分辨光发射光谱测量，他们发现随着温度的降低，材料经历了金属-绝缘体转变。在低温区，他们观察到了开放能隙、能带的重整化以及复本能带的出现，这表明在基态形成了电荷密度波。拉曼光谱分析未发现晶格畸变的迹象。此外，少量电子掺杂显著提高了转变温度，这是因为屏蔽效应的降低使得电子和空穴的载流子密度更加平衡。
这些结果表明，低维HfTe2中电荷密度波的形成机制与激子绝缘体相一致，且不涉及任何结构修饰。
据悉，在固体中，具有有限动量的电子和空穴对的凝聚导致一种称为电荷密度波的有序状态，其中电荷具有空间调制。然而，晶格对称破缺和伴随而来的改变电荷分布的离子的重定位也可能同时发生，这使得很难解开跃迁的起源。
附：英文原文
Title: Observation of possible excitonic charge density waves and metal–insulator transitions in atomically thin semimetals
Author: Gao, Qiang, Chan, Yang-hao, Jiao, Pengfei, Chen, Haiyang, Yin, Shuaishuai, Tangprapha, Kanjanaporn, Yang, Yichen, Li, Xiaolong, Liu, Zhengtai, Shen, Dawei, Jiang, Shengwei, Chen, Peng
Issue&Volume: 2024-01-23
Abstract: In solids, the condensation of electron and hole pairs with finite momentum leads to an ordered state known as a charge density wave, in which the charge has spatial modulation. However, lattice symmetry breaking and the accompanying relocation of the ions, which changes the charge distribution, can also occur simultaneously, making it difficult to disentangle the origin of the transition. Here we demonstrate a condensed phase in low-dimensional HfTe2. Angle-resolved photoemission spectroscopy measurements reveal a metal–insulator transition upon lowering the temperature. The observation of an opening gap, the renormalization of the bands and the emergence of replica bands in the low-temperature regime suggests that a charge density wave formed in the ground state. Raman spectroscopy shows no sign of lattice distortion within the detection limit. A small amount of electron doping substantially raises the transition temperature due to a reduced screening effect and a more balanced carrier density for electrons and holes. Our results indicate that the formation mechanism of the charge density wave is consistent with the excitonic insulator phase in low-dimensional HfTe2 without any structural modification.
DOI: 10.1038/s41567-023-02349-0
Source: https://www.nature.com/articles/s41567-023-02349-0