Discovery of a topological exciton insulator with tunable momentum order

• URL: http://arxiv.org/abs/2312.15862v1
• Date: Tue, 26 Dec 2023 03:05:10 GMT
• Title: Discovery of a topological exciton insulator with tunable momentum order
• Authors: Md Shafayat Hossain, Tyler A. Cochran, Yu-Xiao Jiang, Songbo Zhang, Huangyu Wu, Xiaoxiong Liu, Xiquan Zheng, Byunghoon Kim, Guangming Cheng, Qi Zhang, Maksim Litskevich, Junyi Zhang, Zi-Jia Cheng, Jinjin Liu, Jia-Xin Yin, Xian P. Yang, Jonathan Denlinger, Massimo Tallarida, Ji Dai, Elio Vescovo, Anil Rajapitamahuni, Hu Miao, Nan Yao, Yingying Peng, Yugui Yao, Zhiwei Wang, Luis Balicas, Titus Neupert, M. Zahid Hasan
• Abstract summary: Topology and correlations are fundamental concepts in modern physics, but their simultaneous occurrence within a single quantum phase is exceptionally rare. We present the discovery of such a phase of matter in Ta2Pd3Te5, a semimetal where the Coulomb interaction between electrons and holes leads to the formation of excitonic bound states below T=100 K. Our spectroscopy unveils the development of an insulating gap stemming from the condensation of these excitons, thus giving rise to a highly sought-after correlated quantum phase known as the excitonic insulator.
• Score: 7.605112731805254
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Topology and correlations are fundamental concepts in modern physics, but their simultaneous occurrence within a single quantum phase is exceptionally rare. In this study, we present the discovery of such a phase of matter in Ta2Pd3Te5, a semimetal where the Coulomb interaction between electrons and holes leads to the spontaneous formation of excitonic bound states below T=100 K. Our spectroscopy unveils the development of an insulating gap stemming from the condensation of these excitons, thus giving rise to a highly sought-after correlated quantum phase known as the excitonic insulator. Remarkably, our scanning tunneling microscopy measurements reveal the presence of gapless boundary modes in the excitonic insulator state. Their magnetic field response and our theoretical calculations suggest a topological origin of these modes, rendering Ta2Pd3Te5 as the first experimentally identified topological excitonic insulator in a three-dimensional material not masked by any structural phase transition. Furthermore, our study uncovers a secondary excitonic instability below T=5 K, which differs from the primary one in having finite momentum. We observe unprecedented tunability of its wavevector by an external magnetic field. These findings unlock a frontier in the study of novel correlated topological phases of matter and their tunability.

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