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Visualization of Topological Boundary Modes Manifesting Topological Nodal-Point Superconductivity
The extension of the topological classification of band insulators to topological semimetals gave way to the topology classes of Dirac, Weyl, and nodal line semimetals with their unique Fermi arc and drum head boundary modes. Similarly, there are several suggestions to employ the classification of topological superconductors for topological nodal superconductors with Majorana boundary modes. Here, we show that the surface 1H termination of the transition metal dichalcogenide compound 4Hb-TaS2, in which 1T-TaS2 and 1H-TaS2 layers are interleaved, has the phenomenology of a topological nodal point superconductor. We find in scanning tunneling spectroscopy a residual density of states within the superconducting gap. An exponentially decaying bound mode is imaged within the superconducting gap along the boundaries of the exposed 1H layer characteristic of a gapless Majorana edge mode. The anisotropic nature of the localization length of the edge mode aims towards topological nodal superconductivity. A zero-bias conductance peak is further imaged within fairly isotropic vortex cores. All our observations are accommodated by a theoretical model of a two-dimensional nodal Weyl-like superconducting state, which ensues from inter-orbital Cooper pairing. The observation of an intrinsic topological nodal superconductivity in a layered material will pave the way for further studies of Majorana edge modes and its applications in quantum information processing.N.A., H.B., and B.Y acknowledge the GermanāIsraeli Foundation for Scientiļ¬c Research
and Development (GIF grant no. I-1364-303.7/2016). H.B. and N.A. acknowledge the
European Research Council (ERC, project no. TOPO NW), B.Y. acknowledges ļ¬nancial
support by the Willner Family Leadership Institute for the Weizmann Institute of Sci-
ence, the Benoziyo Endowment Fund for the Advancement of Science, the Ruth and Her-
man Albert Scholars Program for New Scientists, and the Israel Science Foundation (ISF
1251/19). G.A.F. gratefully acknowledges partial support from the National Science Foun-
dation through NSF Grant no. DMR-1720595, and DMR-1949701. Y.O. acknowledges
partial support through the ERC under the European Unionās Horizon 2020 research and
innovation programme (grant agreement LEGOTOP No 788715), the ISF Quantum Science
and Technology (2074/19), the BSF and NSF (2018643), and the CRC/Transregio 183. A.K.
acknowledges the Israel Science Foundation (ISF 320/17).Center for Dynamics and Control of Material