PGI-1 Talk: Yichen Zhang

Quantum Theory of Materials Seminar

Topological crossings in density wave materials probed by angle-resolved photoemission

Recent years of condensed matter physics history has witnessed the “topological revolution” sparked by fundamental symmetry considerations on the electronic band structure. In density wave materials, charge and spin of electrons may regroup to form super periodicities distinct from the original crystal structures, giving rise to new symmetries fostering correlated topological phases. In this talk, based on a series of angle-resolved photoemission spectroscopy (ARPES) studies, of which the understanding is aided by first-principles approaches, we will first introduce an example of charge order induced Dirac pockets in TaTe4 [1], followed by the experimental discovery of Kramers nodal lines in SmAlSi [2], a noncentrosymmetric Weyl semimetal that develops helical magnetic order as the ground state, where the relationship between the Weyl fermions and the magnetic ground state has been clarified in recent theoretical studies [3]. Furthermore, an ideal Kramers nodal line metal consisting of disordered intercalated In layer and 1H-TaS2 layer has been demonstrated to show large Ising-type pseudospin splitting and degenerate topological nodal lines at the Fermi level protected by the achiral little group symmetry [4] through spin-resolved ARPES and state-of-the-art one-step calculation, harboring potential applications regarding spintronics and valleytronics.

If time permitting, I will also briefly introduce recent instrumentation development on applying in-situ magnetic field in ARPES experiments [5], which may enable new degrees of tuning knobs of visualizing band dispersions in various magnetic, topological, and two-dimensional materials.

[1] Y. Zhang, et al., Phys. Rev. B. 108, 155121 (2023).
[2] Y. Zhang, et al., Commun. Phys. 6, 134 (2023).
[3] J. Bouaziz, et al., arxiv. 2311. 07256.
[4] Y. Zhang, et al., in preparation.
[5] J. Huang, et al., Rev. Sci. Instrum. 94, 093902 (2023).

Contact

Prof. Dr. Stefan Blügel
Phone: +49 2461 61-4249
Email: s.bluegel@fz-juelich.de

Yichen Zhang
Department of Physics and Astronomy, Rice University
Email: yz155@rice.edu