Steffen Wiedmann,High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Nijmegen, the Netherlands

Thursday March . 04 2021, 2:00 PM

Unravelling the properties of topological matter in high magnetic fields

Topology in condensed matter physics has become a thriving research
field in the past two decades with the discovery of different classes
of materials such as topological insulators, Weyl and Dirac
semimetals. High magnetic fields play an important role to determine
the charge carrier properties, Fermi surface, or peculiar phenomena
that arise from the underlying band structure of these materials.

One particular class of materials are nodal-line semimetals (NLSMs).
The band structure of these materials is characterized by the
degeneracy of conduction and valence bands along a closed loop in the
three-dimensional Brillouin zone [1]. In many cases, they not only
represent ideal systems with which to investigate the properties of
charge carriers with a linear dispersion relation, they also have the
potential to create a platform for research on topological correlated
matter [2].

In my presentation, I will introduce topological matter and show
recent results on quantum oscillatory phenomena that occur in NLSMs in
high magnetic fields up to 35 T with the focus on the compound ZrSiS.
The Fermi surface topology of these materials is determined by means
of de Haas–van Alphen and Shubnikov-de Haas quantum oscillations in a
full angle-dependent study. Comparison of our experimental
observations with theoretical predictions provides us with a full
picture of the electronic ground state [2-4]. In case the magnetic
field is applied parallel to the /c/-axis of the crystals, a complex
oscillation spectrum evolves above a threshold magnetic field
originating from individual electron and hole pockets as well as from
magnetic breakdown between them. The magnetic breakdown orbits can be
seen as a manifestation of Klein tunneling in momentum space, although
in a regime of partial transmission due to a small but finite
spin-orbit gap between adjacent pockets. Additional high-frequency
quantum oscillations signify magnetic breakdown orbits that encircle
the entire Dirac nodal loop. Furthermore, I will show that quantum
oscillations in resistivity persist up to high temperatures in ZrSiS
that are attributed to Stark interference between orbits of nearly
equal masses [4].

Finally, I will address novel experimental techniques, transport under
uniaxial strain and strain dilatometry, that we are currently
developing at the HFML that will enable us to tune the fundamental
properties of topological and correlated matter in high magnetic fields.

[1]C. Fang /et al., /Chinese Phys. B *25*, 117106 (2016).

[2]S. Pezzini /et al., /Nature Physics *14*, 178 (2018).

[3]M. van Delft /et al.,/ Phys. Rev. Lett. *121*, 256602 (2018).

[4]C. S. A. Müller /et al.,/ Phys. Rev. Research *2*, 023217 (2020).

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