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Due to their intrinsic topology,Weyl semimetals are potential candidates for topological superconductivity, but so far have always been connected with bulk superconductivity, leaving the possibility of intrinsic superconductivity of their topological surface states, the Fermi arcs, practically without attention, even from the theory side. By means of angle-resolved photoemission spectroscopy (ARPES) and ab initio calculations, we identify topological Fermi arcs on two opposing surfaces of the non-centrosymmetric Weyl material trigonal PtBi2. We show these states become superconducting at temperatures around 10 K. Remarkably, the corresponding coherence peaks appear as the strongest and sharpest excitations ever detected by photoemission from solids. Superconductivity is also found in our STM measurements showing in addition spatial inhomogeneity of the superconducting gap. In some samples superconducting gaps as large as 20 meV are revealed by STM resembling the phenomenology found in high-Tc superconductors. However bulk probes such as magnetization, transport and thermodynamics do not show superconductivity. This is consistent with the absence of gaps in bulk electronic states measured by ARPES. Our findings indicate that superconductivity in PtBi2 can occur exclusively at the surface, rendering it a possible platform to host Majorana modes in intrinsically topological superconductor–normal metal–superconductor junctions.

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Bernd Büchner (SFB1238/Kolloquium), IFW Dresden
Seminar Room of the Theory Institute (old building)
Contact: Markus Braden