Evidence of superconducting Fermi arcs.

An essential ingredient for the production of Majorana fermions for use in quantum computing is topological superconductivity1,2 . As bulk topological superconductors remain elusive, the most promising approaches exploit proximity-induced superconductivity3 , making systems fragile and difficult to realize4-7 . Due to their intrinsic topology8 , Weyl semimetals are also potential candidates1,2 , but 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. Here, by means of angle-resolved photoemission spectroscopy and ab initio calculations, we identify topological Fermi arcs on two opposing surfaces of the non-centrosymmetric Weyl material trigonal PtBi2 (ref. 9 ). 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. 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 Josephson junctions.