Guest seminar hosted by CDQT.
Speaker: Prof. Jeroen van den Brink (Institute for Theoretical Solid State Physics, IFW Dresden)
Title: Topological surface superconductivity in PtBi2

Abstract:
Most superconducting materials are well understood and conventional—that is, the pairs of electrons that cause the superconductivity by their condensation have the highest possible symmetry. Famous exceptions are the enigmatic high-temperature (high-Tc) cuprate superconductors. Nodes in their superconducting gap are the fingerprint of their unconventional character and imply superconducting pairing of d-wave symmetry. Here, by using angle-resolved photoemission spectroscopy, we observe that the Weyl semimetal PtBi2 [1,2] harbours nodes in its superconducting gap, implying unconventional i-wave pairing symmetry. At temperatures below 10 K, the superconductivity in PtBi2 gaps out its topological surface states, the Fermi arcs, whereas its bulk states remain normal [3]. The nodes in the superconducting gap that we observe are located exactly at the centre of the Fermi arcs and imply the presence of topologically protected Majorana cones around this locus in momentum space [4]. From this, we infer theoretically that robust zero-energy Majorana flat bands emerge at surface step edges. This establishes PtBi2 surfaces not only as unconventional, topological i-wave superconductors but also as a promising material platform in the ongoing effort to generate and manipulate Majorana bound states.

1.      Vocaturo, Koepernik, Facio, Timm, Fulga, Janson, JvdB, Phys. Rev. B 110, 054504 (2024).
2.      Veyrat, Labracherie, Bashlakov, Caglieris, Facio, Shipunov, Charvin, Acharya, Naidyuk, Giraud, JvdB, Buchner, Hess, Aswartham, Dufouleur, Nano Lett. 23, 1229 (2023).
3.      Kuibarov, Suvorov, Vocaturo, Fedorov, Lou, Merkwitz, Voroshnin, Facio, Koepernik, Yaresko, Shipunov, Aswartham, JvdB, Buchner, Borisenko, Nature 626, 294 (2024).
4.      Changdar, Suvorov, Kuibarov, Thirupathaiah, Shipunov, Aswartham, Wurmehl, Kovalchuk, Koepernik, Timm, Büchner, Fulga, Borisenko, JvdB, Nature 647, 613 (2025)

About the speaker:
Jeroen van den Brink is a Dutch theoretical condensed matter physicist renowned for his contributions to the understanding of strongly correlated quantum materials. Since 2009, he has served as the Director of the Institute for Theoretical Solid State Physics at the Leibniz Institute for Solid State and Materials Research (IFW) in Dresden, Germany. He also holds a professorship in solid-state theory at the Dresden University of Technology. His research focuses on theoretical condensed matter physics, particularly electronic structure theory, correlated electron systems, topological states of matter, and the theory of quantum matter. His work has earned him several accolades, including the Humboldt Research Prize in 2018 and the Van der Waals Professorial Chair at the University of Amsterdam in 2020.