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Emergence of Nontrivial Low-Energy Dirac Fermions in Antiferromagnetic EuCd2As2 |
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| Authors: | Junzhang Ma Han Wang Simin Nie Changjiang Yi Yuanfeng Xu Hang Li Jasmin Jandke Wulf Wulfhekel Yaobo Huang Damien West Pierre Richard Alla Chikina Vladimir N. Strocov Joël Mesot Hongming Weng Shengbai Zhang Youguo Shi Tian Qian Ming Shi Hong Ding |
| Affiliation: | 1. Paul Scherrer Institute, Swiss Light Source, CH-5232 Villigen, PSI, Switzerland;2. Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, NY, 12180 USA;3. Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305 USA;4. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 China School of Physics, University of Chinese Academy of Sciences, Beijing, 100190 China;5. Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany;6. Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201204 China;7. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 China School of Physics, University of Chinese Academy of Sciences, Beijing, 100190 China Institut quantique, Université de Sherbrooke, 2500 boulevard de l'Université, Sherbrooke, Québec, J1K 2R1 Canada;8. Paul Scherrer Institute, Swiss Light Source, CH-5232 Villigen, PSI, Switzerland Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne, CH-10 15 Lausanne, Switzerland;9. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 China Songshan Lake Materials Laboratory Dongguan, Guangdong, 523808 China;10. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 China;11. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190 China School of Physics, University of Chinese Academy of Sciences, Beijing, 100190 China Songshan Lake Materials Laboratory Dongguan, Guangdong, 523808 China CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100190 China |
| Abstract: | Parity-time symmetry plays an essential role for the formation of Dirac states in Dirac semimetals. So far, all of the experimentally identified topologically nontrivial Dirac semimetals (DSMs) possess both parity and time reversal symmetry. The realization of magnetic topological DSMs remains a major issue in topological material research. Here, combining angle-resolved photoemission spectroscopy with density functional theory calculations, it is ascertained that band inversion induces a topologically nontrivial ground state in EuCd2As2. As a result, ideal magnetic Dirac fermions with simplest double cone structure near the Fermi level emerge in the antiferromagnetic (AFM) phase. The magnetic order breaks time reversal symmetry, but preserves inversion symmetry. The double degeneracy of the Dirac bands is protected by a combination of inversion, time-reversal, and an additional translation operation. Moreover, the calculations show that a deviation of the magnetic moments from the c-axis leads to the breaking of C3 rotation symmetry, and thus, a small bandgap opens at the Dirac point in the bulk. In this case, the system hosts a novel state containing three different types of topological insulator: axion insulator, AFM topological crystalline insulator (TCI), and higher order topological insulator. The results provide an enlarged platform for the quest of topological Dirac fermions in a magnetic system. |
| Keywords: | axion insulator condensed matter physics higher order topological insulator magnetic Dirac semimetal |