Energy dependent spatial texturing in the CDW of 1T-Cu_xTiSe₂

The competition between ground states is a central topic in modern condensed matter physics. It is of common belief that unconventional superconductivity (SC) emerges from a precursor state, which is suppressed upon the appearance of the superconducting condensate.
Since the discovery of a Charge Density Wave (CDW) and Cu doping induced SC in TiSe₂, this system has become prototypical for studying the interplay between these two states by means of scanning tunneling microscopy.
While the SC in Cu_xTiSe₂ seems to follow a standard BCS behaviour, the microscopic origin of the CDW is still under debate. In order to address this issue, we performed a detailed STM/STS study of the impact of Cu intercalation on the CDW in Cu_xTiSe₂.
The CDW modulation is found to break up in a complex energy and position-dependent texture, which is explained in terms of charge inhomogeneities induced by Cu intercalation. Under certain conditions, the CDW is visible and well developed in all the crystals investigated, including the superconducting ones, suggesting a possible coexistence of SC and CDW order. These findings further invalidate both Fermi surface nesting and excitonic pairing as the primary CDW formation mechanism in this material.