Spin fluctuation induced Weyl semimetal state in the paramagnetic phase of EuCd<sub>2</sub>As<sub>2</sub>

J. Z. Ma, S. M. Nie, C. J. Yi, J. Jandke, T. Shang, M. Y. Yao, M. Naamneh, L. Q. Yan, Y. Sun, A. Chikina, V. N. Strocov, M. Medarde, M. Song, Y. M. Xiong, G. Xu, W. Wulfhekel, J. Mesot, M. Reticcioli, C. Franchini, C. Mudry, M. Müller, Y. G. Shi, T. Qian, H. Ding, M. Shi

Weyl fermions as emergent quasiparticles can arise in Weyl semimetals (WSMs) in which the energy bands are nondegenerate, resulting from inversion or time-reversal symmetry breaking. Nevertheless, experimental evidence for magnetically induced WSMs is scarce. Here, using photoemission spectroscopy, we observe that the degeneracy of Bloch bands is already lifted in the paramagnetic phase of EuCd2As2. We attribute this effect to the itinerant electrons experiencing quasi-static and quasi–long-range ferromagnetic fluctuations. Moreover, the spin-nondegenerate band structure harbors a pair of ideal Weyl nodes near the Fermi level. Hence, we show that long-range magnetic order and the spontaneous breaking of time-reversal symmetry are not essential requirements for WSM states in centrosymmetric systems and that WSM states can emerge in a wider range of condensed matter systems than previously thought.

Computational Materials Physics
External organisation(s)
Paul Scherrer Institute, Stanford University, Songshan Lake Materials Laboratory, University of Science and Technology of China (USTC), Collaborative Innovation Center of Advanced Microstructures, Huazhong University of Science and Technology, Eidgenössische Technische Hochschule Zürich, Università degli Studi di Bologna, École polytechnique fédérale de Lausanne, Chinese Academy of Sciences (CAS), Karlsruher Institut für Technologie, University of the Chinese Academy of Sciences
Science Advances
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Peer reviewed
Austrian Fields of Science 2012
Solid state physics
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