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Optical signatures of multifold fermions in the chiral topological semimetal CoSi

  • Xu, Bing Fribourg Center for Nanomaterials, Department of Physics, University of Fribourg, CH-1700 Fribourg, Switzerland
  • Fang, Zhenyao Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
  • Sánchez-Martínez, Miguel-Angel Institut Néel, CNRS and Université Grenoble Alpes, 38042 Grenoble, France
  • Venderbos, Jorn W. F. Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA - Department of Physics, Drexel University, Philadelphia, PA 19104, USA - Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104, USA
  • Ni, Zhuoliang Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
  • Qiu, Tian Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
  • Manna, Kaustuv Max Planck Institut fur Chemische Physik fester Stoffe, 01187 Dresden, Germany
  • Wang, Kefeng Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA
  • Paglione, Johnpierre Maryland Quantum Materials Center, Department of Physics, University of Maryland, College Park, MD 20742, USA - Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
  • Bernhard, Christian Fribourg Center for Nanomaterials, Department of Physics, University of Fribourg, CH-1700 Fribourg, Switzerland
  • Felser, Claudia Max Planck Institut fur Chemische Physik fester Stoffe, 01187 Dresden, Germany - Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
  • Mele, Eugene J. Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
  • Grushin, Adolfo G. Institut Néel, CNRS and Université Grenoble Alpes, 38042 Grenoble, France
  • Rappe, Andrew M. Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
  • Wu, Liang Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
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    03.11.2020
Published in:
  • Proceedings of the National Academy of Sciences. - 2020, vol. 117, no. 44, p. 27104–27110
English We report the optical conductivity in high-quality crystals of the chiral topological semimetal CoSi, which hosts exotic quasiparticles known as multifold fermions. We find that the optical response is separated into several distinct regions as a function of frequency, each dominated by different types of quasiparticles. The low-frequency intraband response is captured by a narrow Drude peak from a high-mobility electron pocket of double Weyl quasiparticles, and the temperature dependence of the spectral weight is consistent with its Fermi velocity. By subtracting the low-frequency sharp Drude and phonon peaks at low temperatures, we reveal two intermediate quasilinear interband contributions separated by a kink at 0.2 eV. Using Wannier tight-binding models based on first-principle calculations, we link the optical conductivity above and below 0.2 eV to interband transitions near the double Weyl fermion and a threefold fermion, respectively. We analyze and determine the chemical potential relative to the energy of the threefold fermion, revealing the importance of transitions between a linearly dispersing band and a flat band. More strikingly, below 0.1 eV our data are best explained if spin-orbit coupling is included, suggesting that at these energies, the optical response is governed by transitions between a previously unobserved fourfold spin-3/2 node and a Weyl node. Our comprehensive combined experimental and theoretical study provides a way to resolve different types of multifold fermions in CoSi at different energy. More broadly, our results provide the necessary basis to interpret the burgeoning set of optical and transport experiments in chiral topological semimetals.
Faculty
Faculté des sciences et de médecine
Department
Département de Physique
Language
  • English
Classification
Physics
License
License undefined
Identifiers
Persistent URL
https://folia.unifr.ch/unifr/documents/308949
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