Superconducting dome by tuning through a van Hove singularity in a two-dimensional metal

Chemical substitution is a promising route for the exploration of a rich variety of doping- and/or disorder-dependent collective phenomena in low-dimensional quantum materials. Here we show that transition metal dichalcogenide alloys are ideal platforms to this purpose. In particular, we demonstrate the emergence of superconductivity in the otherwise metallic single-layer TaSe_2 by minute electron doping provided by substitutional W atoms. We investigate the temperature and magnetic field dependence of the superconducting state of Ta_1-δW_δSe_2 with electron doping ( δ ) using variable temperature (0.34–4.2 K) scanning tunneling spectroscopy (STS). We unveil the emergence of a superconducting dome spanning 0.003 < δ < 0.03 with a maximized critical temperature of 0.9 K, a significant increase from that of bulk TaSe_2 ( T _C = 0.14 K). Superconductivity emerges from an increase of the density of states (DOS) as the Fermi surface approaches a van Hove singularity due to doping. Once the singularity is reached, however, the DOS decreases with δ , which gradually weakens the superconducting state, thus shaping the superconducting dome. Lastly, our doping-dependent measurements suggest the development of a Coulomb glass phase triggered by disorder due to W dopants.