The chiral anomaly, screening and low energy electron dynamics of Weyl semimetals

• Applicant: Professor Dr. Peter Lemmens
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 346795687

• Final Report Year: 2022

Final Report Abstract

Topology is a mathematical concept that has important implications in many fields of natural sciences. We have investigated several Weyl semimetals with linear dispersing, itinerant electronic states and that cross at degeneracy points of different chirality. We have also taken topological spin systems into our repertoire. This is due to several similarities that Weyl and spin liquids share. These similarities are the bulk to surface correspondence of some topological states as well as aspects of fractionalization. Topology as spin coordination in space is interesting to control the low-energy dynamics and quasiparticle interactions. As we are interested in a unifying understanding and not in materials peculiarities, a limitation to a single compound is counterproductive. Our spectroscopic Raman scattering study shows that magnetic fields can be used to control the dynamics and interactions. In the Weyl semimetal PdGa we found low energy interband scattering that is induced by magnetic fields of the right orientation with respect to the chirality of the sample and the incident circular polarized light. This scattering is supposed to be related to the chiral anomaly. In addition there exist phonon scattering with an unconventional directionality. This effect is described in analogy to the Hanle effect of resonant X-Ray scattering. In several spin liquid systems of Kitaev and of Heisenberg type we identify fingerprints of fractionalization of excitations that can be affected by magnetic fields. In an interacting spin chain system of Haldane type light-induced fractionalization. The latter is characterized by a temperature dependence of the corresponding scattering intensity that is described by a Fermionic statistics. During the project we noticed a large sensitivity of the physical properties of Weyl semimetals on small variations of structure and composition. This effect can be understood as being based on the singular electronic band structure with Fermi energies close to the degeneracy points. This observation is also consistent with the promising catalytic activity of surfaces of Weyl semimetals. During the project the B. I. Verkin price of the National Academy of Science of Ukraine (2020) has been assigned jointly to the PI and the collaboration partners Dr. V. Gnezdilov (Kharkiv) and Prof. Dr. Yu. Pashkevich (Kiev).

Publications

• Relation between Kitaev magnetism and structure in α-RuCl3, Phys. Rev. B 95, 174429 (2017)
  A. Glamazda, P. Lemmens, S.-H. Do, Y. S. Kwon, and K.-Y. Choi
  
• Flat-band spin dynamics and phonon anomalies of the saw-tooth spin-chain system Fe2O(SeO3)2, Phys. Rev. B 99, 064413 (2019)
  V. P. Gnezdilov, Yu. G. Pashkevich, V. S. Kurnosov, O. V. Zhuravlev, D. Wulferding, P. Lemmens, D. Menzel, E. S. Kozlyakova, A. N. Vasiliev, A. Yu. Akhrorov, E. S. Kuznetsova, P. S. Berdonosov, and V. A. Dolgikh
  
• Effect of topology on quasi-particle interactions in the Weyl semimetal WP2, Phys. Rev. B 102, 075116 (2020)
  D. Wulferding, P. Lemmens, F. Büscher, D. Schmeltzer, C. Felser, Ch. Shekhar
  
• Kitaev Spin Liquid Candidate OsxCl3 Comprising a Highly Disordered Honeycomb Lattice, J. Phys. Soc. Jpn. 89, 114709 (2020)
  K. Kataoka, D. Hirai, T. Yajima, D. Nishio-Hamane, R. Ishii, K.-Y. Choi, D. Wulferding, P. Lemmens, S. Kittaka, T. Sakakibara, H. Ishikawa, A. Matsuo, K. Kindo, and Z. Hiroi
  
• Magnon bound states vs. anyonic Majorana excitations in the Kitaev honeycomb magnet α-RuCl3, Nat. Communications 11, 1603 (2020)
  D. Wulferding, Y.-S. Choi, S.-H. Do, Ch. H. Lee, P. Lemmens, C. Faugeras, Y. Gallais, and K.-Y. Choi
  
• Unconventional spin excitations in the S = 3/2 triangular antiferromagnet RbAg2Cr[VO4]2, Phys. Rev. B 101, 224420 (2020)
  S. Lee, R. Klauer, J. Menten, H. Luetkens, P. Lemmens, A. Möller, and K.-Y. Choi
  
• Non-Abelian statistics in light scattering processes across interacting Haldane chains, Phys. Rev. B 104, 165118, (2021)
  V. Gnezdilov, V. Kurnosov, Yu. G. Pashkevich, A. K. Bera, A. T. M. N. Islam, B. Lake, B. Lobbenmeier, D. Wulferding, P. Lemmens
  
• Raman scattering of plane–wave and twisted light off chiral molecular liquids, Low Temp. Phys. 47, 959 (2021)
  F. Büscher, S. Müllner, D. Wulferding, Yu. G. Pashkevich, V. Gnezdilov, A. A. Peshkov, A. Surzhykov, and P. Lemmens
  
• Thermally populated vs. field-induced triplon bound states in the Shastry-Sutherland lattice SrCu2(BO3)2, NPJ Quantum Materials 6, 102 (2021)
  D. Wulferding, Y. Choi, S. Lee, M. Prosnikov, Y. Gallais, P. Lemmens, C. Zhong, H. Kageyama, and K.-Y. Choi