DOE OSTI · 2574311
Topological excitonic insulator with tunable momentum order
Abstract
Correlated topological materials often maintain a delicate balance among physical symmetries. Many topological orders are symmetry protected, whereas most correlated phenomena arise from spontaneous symmetry breaking. Cases where symmetry breaking induces a non-trivial topological phase are rare. Here we demonstrate the presence of two such phases in Ta 2 Pd 3 Te 5 , where Coulomb interactions form excitons that condense below 100 K, one with zero and the other with finite momentum. We observed a full spectral bulk gap, which stems from exciton condensation. This topological excitonic insulator state spontaneously breaks mirror symmetries but involves a weak structural coupling. Scanning tunnelling microscopy shows gapless boundary modes in the bulk insulating phase. Their magnetic field response, together with theoretical modelling, indicates a topological origin. These observations establish Ta 2 Pd 3 Te 5 as a topological excitonic insulator in a three-dimensional crystal. Finally, our results manifest a unique sequence of topological exciton condensations in a bulk crystal, offering exciting opportunities to study critical behaviour and excitations.
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Hossain, Md Shafayat [University of California, Los Angeles, CA (United States); Princeton University, NJ (United States)] (ORCID:0000000237445877), Cheng, Zi-Jia [Princeton University, NJ (United States)] (ORCID:0000000294737753), Jiang, Yu-Xiao [Princeton University, NJ (United States)] (ORCID:0000000279583100), Cochran, Tyler A. [Princeton University, NJ (United States)] (ORCID:0000000317458467), Zhang, Song-Bo [Hefei National Laboratory (China); University of Zurich (Switzerland)] (ORCID:0000000242704597), Wu, Huangyu [Beijing Institute of Technology (China); Chinese Academy of Sciences, Beijing (China)], Liu, Xiaoxiong [University of Zurich (Switzerland); Southern University of Science and Technology (SUSTech), Shenzhen (China); Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen (China); Shenzhen Key Laboratory of Quantum Science and Engineering (China); International Quantum Academy, Shenzhen (China)] (ORCID:0000000221870035), Zheng, Xiquan [Peking University, Beijing (China)], Cheng, Guangming [Princeton University, NJ (United States)] (ORCID:0000000158521341), Kim, Byunghoon [Princeton University, NJ (United States)] (ORCID:0000000189494833), Zhang, Qi [Princeton University, NJ (United States)], Litskevich, Maksim [Princeton University, NJ (United States)] (ORCID:0000000330496521), Zhang, Junyi [Johns Hopkins University, Baltimore, MD (United States)] (ORCID:0000000333061654), Liu, Jinjin [Beijing Institute of Technology (China); Chinese Academy of Sciences, Beijing (China)], Yin, Jia-Xin [Princeton University, NJ (United States)] (ORCID:0000000326614206), Yang, Xian P. [Princeton University, NJ (United States)] (ORCID:000000025019374X), Denlinger, Jonathan D. [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000176451631), Tallarida, Massimo [ALBA Synchrotron Light Source, Barcelona (Spain)] (ORCID:0000000214383466), Dai, Ji [ALBA Synchrotron Light Source, Barcelona (Spain)] (ORCID:0000000313886843), Vescovo, Elio [Brookhaven National Laboratory (BNL), Upton, NY (United States)] (ORCID:0000000303503861), Rajapitamahuni, Anil [Brookhaven National Laboratory (BNL), Upton, NY (United States)], Yao, Nan [Princeton University, NJ (United States)] (ORCID:0000000240811495), Keselman, Anna [Technion – Israel Institute of Technology, Haifa (Israel)], Peng, Yingying [Peking University, Beijing (China)] (ORCID:0000000226573590), Yao, Yugui [Beijing Institute of Technology (China); Chinese Academy of Sciences, Beijing (China)] (ORCID:0000000335443787), Wang, Zhiwei [Beijing Institute of Technology (China); Chinese Academy of Sciences, Beijing (China)] (ORCID:0000000301822471), Balicas, Luis [National High Magnetic Field Laboratory, Tallahassee, FL (United States); Florida State University, Tallahassee, FL (United States)] (ORCID:0000000252090293), Neupert, Titus [University of Zurich (Switzerland)], Hasan, M. Zahid [Princeton University, NJ (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000197303128). 2025-07-11. Topological excitonic insulator with tunable momentum order. https://doi.org/10.1038/s41567-025-02917-6
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