A multipronged investigation of the phase diagram of Cu_xTiSe2

Using a combination of angle resolved photoemission spectroscopy, Scanning Tunneling Spectroscopy (STS), electrical resistivity and magnetization measurements on Cu_xTiSe₂, i.e., copper-intercalated 1T-TiSe_2, we revisit the ramifications of quenched disorders on superconducting (SC) and charge density wave (CDW) orders in the coexistent regime of the phase diagram. With increasing concentration of Cu intercalation, Cu_xTiSe₂ gets structurally disordered, but electronically ordered as evidenced from the decreasing residual resistivity. As in previous studies, we observed that the CDW order gets weakened with increasing x and superconductivity emerges at x~0.04. SC and CDW orders coexist in an extended region of the phase diagram. Unlike in intercalated incommensurate systems, where the CDW is affected by disorder induced phase incoherence of the order parameter, CDW in Cu_xTiSe₂ seems to get affected via suppression in the amplitude of the order parameter. Contrary to the common notion of inevitable competition between proximate CDW and SC states that generates granular orders, we observe direct evidence for spatially homogenous superconductivity even at the presence of well-defined CDW correlations. The coexistence of SC and CDW orders can probably be tied to the involvement of multiple bands in these orderings, while the spatial uniformity of the SC order is most likely a consequence of the huge discrepancy between the SC coherence length and the electronic mean free path.