Emergence of Fermi Pockets in a New Excitonic Charge-Density-Wave Melted Superconductor

A superconducting state (T_c∼4.2  K) has very recently been observed upon successful doping of the charge-density-wave (CDW) ordered triangular lattice TiSe_2, with copper. Using state-of-the-art photoemission spectroscopy we identify, for the first time, momentum-space locations of doped electrons that form the Fermi sea of the superconductor. With doping, we find that kinematic nesting volume increases, whereas coherence of the CDW collective order sharply drops. In superconducting doping, as chemical potential rises, we observe the emergence of a large density of states in the form of a narrow electron pocket near the L point of the Brillouin zone with d-like character. The k-space spectral evolution directly demonstrates, for the first time, that the CDW order parameter microscopically competes with superconductivity in the same band.