The TRR 227 kindly invites you to the joint Colloquium of the TRR 227 & FU Physics Department.

*Speaker:*

Dr. Niels Schröter, Max-Planck-Institut für Mikrostrukturphysik, Schröter Lab for Quantum Materials & Technologies (Halle, Saale)

*Title:*

**Chiral topological semimetals: Next-generation quantum materials at the intersection of topology, correlations, and magnetism**

*Abstract*

The term chirality is derived from the Greek word for ‘hand’ χειρ (kheir) and generally describes objects that are distinct from their mirror image. It is long known that chirality plays a crucial role in nature, providing powerful functionality to chiral molecules in living organisms. Our goal is to extend this concept from the molecular to the solid state to discover new chirality-enabled functionalities in crystals that could form the basis for new technologies. One particular focus is on chiral topological semimetals, a new class of quantum materials at the intersection of structural and electronic chirality. We discovered the first example of this material class a few years ago [1] and have since demonstrated that they host new fermionic quasiparticles without analogue in high-energy physics, which carry large and controllable topological charges [2].

In this talk, I will present new results beyond these initial works and demonstrate that these materials realise an isotropic parallel spin-momentum locking that can be considered the natural counterpart of Rashba spin-orbit coupling [3]. Moreover, I will also present fingerprints of parallel locking of the linear momentum to the orbital angular momentum [4]. If there is time, I will also discuss magnetic chiral topological semimetals and the effect of spin-dependent correlations on the quasiparticle lifetimes of bulk and chiral surface states. I may also comment on our latest attempts to visualize the surface states in nodal superconductors.

[1] N. B. M. Schröter, D. Pei, M. G. Vergniory, Y. Sun, K. Manna, F. de Juan, J. A. Krieger, V. Süss, M. Schmidt, P. Dudin, B. Bradlyn, T. K. Kim, T. Schmitt, C. Cacho, C. Felser, V. N. Strocov, Y. Chen, "Chiral topological semimetal with multifold band crossings and long Fermi arcs". Nat. Phys. **15**, 759–765 (2019)

[2] N. B. M. Schröter, S. Stolz, K. Manna, F. de Juan, M. G. Vergniory, J. A. Krieger, D. Pei, T. Schmitt, P. Dudin, T. K. Kim, C. Cacho, B. Bradlyn, H. Borrmann, M. Schmidt, R. Widmer, V. N. Strocov, C. Felser, "Observation and control of maximal Chern numbers in a chiral topological semimetal". Science **369**, 179–183 (2020)

[3] J. A. Krieger, S. Stolz, I. Robredo, K. Manna, E. C. McFarlane, M. Date, E. B. Guedes, J. H. Dil, C. Shekhar, H. Borrmann, Q. Yang, M. Lin, V. N. Strocov, M. Caputo, B. Pal, M. D. Watson, T. K. Kim, C. Cacho, F. Mazzola, J. Fujii, I. Vobornik, S. S. P. Parkin, B. Bradlyn, C. Felser, M. G. Vergniory, N. B. M. Schröter, "Parallel spin-momentum locking in a chiral topological semimetal". arXiv:2210.08221, to appear in Nat. Commun. (2024)

[4] Y. Yen, J. A. Krieger, M. Yao, I. Robredo, K. Manna, Q. Yang, E. C. McFarlane, C. Shekhar, H. Borrmann, S. Stolz, R. Widmer, O. Gröning, V. N. Strocov, S. S. P. Parkin, C. Felser, M. G. Vergniory, M. Schüler, N. B. M. Schröter, "Controllable orbital angular momentum monopoles in chiral topological semimetals". arXiv:2311.13217

### Time & Location

May 03, 2024 | 03:15 PM

Lecture Hall A - Physics Department - Freie Universität Berlin

(Arnimallee 14, 14195 Berlin-Dahlem)