近日，美国麻省理工学院的Nuh Gedik及其研究小组取得一项新进展。经过不懈努力，他们直接观测到笼目金属CsV₃Sb₅中的电荷密度波集体模式。相关研究成果已于2023年9月25日在国际知名学术期刊《美国科学院院刊》上发表。

该研究团队使用超短激光脉冲熔化CsV₃Sb₅中的电荷有序态，并利用飞秒角分辨光电发射记录产生的动力学。研究人员解析了电荷有序态的熔化时间，并直接观测了其振幅模式，对可能的最快晶格重排时间施加了基本限制。这些观测与从头算一起为电荷密度波的结构机制而不是电子机制提供了明确的证据。这一研究发现为更好地理解笼目晶格上的非常规相铺平了道路。

据悉，最近发现的一组笼目金属AV₃Sb₅ (A = K, Rb, Cs)表现出各种缠绕在一起的非常规电子相，这些电子相来自令人费解的电荷密度波相。理解这种电荷有序的母相对于破译整个相图至关重要。然而，电荷密度波的机制仍然存在争议，其波动的主要来源-集体模式-尚未被实验观察到。

附：英文原文

Title: Direct observation of the collective modes of the charge density wave in the kagome metal CsV₃Sb₅

Author: Azoury, Doron, von Hoegen, Alexander, Su, Yifan, Oh, Kyoung Hun, Holder, Tobias, Tan, Hengxin, Ortiz, Brenden R., Capa Salinas, Andrea, Wilson, Stephen D., Yan, Binghai, Gedik, Nuh

Issue&Volume: 2023-9-2

Abstract: A recently discovered group of kagome metals AV₃Sb₅ (A = K, Rb, Cs) exhibit a variety of intertwined unconventional electronic phases, which emerge from a puzzling charge density wave phase. Understanding of this charge-ordered parent phase is crucial for deciphering the entire phase diagram. However, the mechanism of the charge density wave is still controversial, and its primary source of fluctuations—the collective modes—has not been experimentally observed. Here, we use ultrashort laser pulses to melt the charge order in CsV₃Sb₅ and record the resulting dynamics using femtosecond angle-resolved photoemission. We resolve the melting time of the charge order and directly observe its amplitude mode, imposing a fundamental limit for the fastest possible lattice rearrangement time. These observations together with ab initio calculations provide clear evidence for a structural rather than electronic mechanism of the charge density wave. Our findings pave the way for a better understanding of the unconventional phases hosted on the kagome lattice.

DOI: 10.1073/pnas.2308588120

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2308588120