Abstract: Most superconducting materials are well-understood and conventional in the sense that the pairs of electrons that cause the superconductivity by their condensation have the highest possible symmetry. Famous exceptions are the enigmatic 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, using angle-resolved photoemission spectroscopy, we observe that the Weyl semimetal PtBi2 harbors nodes in its superconducting gap, implying unconventional i-wave pairing symmetry. At temperatures below 10K, the superconductivity in PtBi2 gaps out its topological surface states, the Fermi arcs, while its bulk states remain normal. The nodes in the superconducting gap that we observe are located exactly at the center of the Fermi arcs, and imply the presence of topologically protected Majorana cones around this locus in momentum space. From this, we infer theoretically that robust zero-energy Majorana flat bands emerge at surface step edges. This not only establishes PtBi2 surfaces as unconventional, topological i-wave superconductors but also as a promising material platform in the ongoing effort to generate and manipulate Majorana bound states.
References:
Changdar, Suvorov, Kuibarov, Thirupathaiah, Shipunov, Aswartham, Wurmehl, Kovalchuk, Koepernik, Timm, Büchner, Fulga, Borisenko, van den Brink
Topological nodal i-wave superconductivity in PtBi2, arXiv:2507.01774
Vocaturo, Koepernik, Facio, Timm, Fulga, Janson, van den Brink
Electronic structure of the surface superconducting Weyl semimetal PtBi2, Phys. Rev. B 110, 054504 (2024)
Kuibarov, Suvorov, Vocaturo, Fedorov, Lou, Merkwitz, Voroshnin, Facio, Koepernik, Yaresko, Shipunov, Aswartham, van den Brink, Buchner, Borisenko
Evidence of superconducting Fermi arcs, Nature 626, 294 (2024).
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