Atomic-Scale Mapping of Superconductivity in the Incoherent CDW Mosaic Phase of a Transition Metal Dichalcogenide.

The emergence of superconductivity in the octahedrally coordinated (1T) phase of TaS is preceded by the loss of long-range order in the charge density wave (CDW). Such decoherence triggers the formation of nm-sized coherent CDW domains bound by a domain wall network, known as the mosaic phase, and proposed as the spatial origin of superconductivity. Here, we report the atomic-scale characterization of superconductivity in 1T-TaSSe, a model 1T compound exhibiting the CDW mosaic phase, using high-resolution scanning tunneling spectroscopy and Andreev spectroscopy. Spatially resolved conductance maps at the onset of superconductivity reveal that the density of states at the Fermi level is mostly localized on the CDW domains rather than at the domain walls, suggesting their dominant role in the formation of superconductivity. This scenario is confirmed at 340 mK, where superconductivity is fully developed, and the subtle spatial inhomogeneity of superconductivity remains unlinked to the domain wall network.