Bretscher Hope M, Andrich Paolo, Murakami Yuta, Golež Denis, Remez Benjamin, Telang Prachi, Singh Anupam, Harnagea Luminita, Cooper Nigel R, Millis Andrew J, Werner Philipp, Sood A K, Rao Akshay
Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.
Sci Adv. 2021 Jul 7;7(28). doi: 10.1126/sciadv.abd6147. Print 2021 Jul.
Excitonic insulators host a condensate of electron-hole pairs at equilibrium, giving rise to collective many-body effects. Although several materials have emerged as excitonic insulator candidates, evidence of long-range coherence is lacking and the origin of the ordered phase in these systems remains controversial. Here, using ultrafast pump-probe microscopy, we investigate the possible excitonic insulator TaNiSe Below 328 K, we observe the anomalous micrometer-scale propagation of coherent modes at velocities of ~10 m/s, which we attribute to the hybridization between phonon modes and the phase mode of the condensate. We develop a theoretical framework to support this explanation and propose that electronic interactions provide a substantial contribution to the ordered phase in TaNiSe These results allow us to understand how the condensate's collective modes transport energy and interact with other degrees of freedom. Our study provides a unique paradigm for the investigation and manipulation of these properties in strongly correlated materials.
激子绝缘体在平衡状态下存在电子 - 空穴对凝聚体，从而产生集体多体效应。尽管已有几种材料成为激子绝缘体候选材料，但缺乏长程相干的证据，并且这些系统中有序相的起源仍存在争议。在此，我们使用超快泵浦 - 探测显微镜研究了可能的激子绝缘体TaNiSe。在328 K以下，我们观察到相干模以约10 m/s的速度在微米尺度上异常传播，我们将其归因于声子模与凝聚体的相位模之间的杂化。我们建立了一个理论框架来支持这一解释，并提出电子相互作用对TaNiSe中的有序相有重大贡献。这些结果使我们能够理解凝聚体的集体模如何传输能量以及与其他自由度相互作用。我们的研究为研究和操纵强关联材料中的这些特性提供了一个独特的范例。
