Discommensuration-driven superconductivity in the charge density wave phases of transition-metal dichalcogenides

We introduce a McMillan-Ginzburg-Landau theory to describe the cooperative coexistence of charge density and superconducting order in two-dimensional crystals. With a free energy that explicitly accounts for the competition between commensurate and incommensurate ground states, we are able to map the transition between these phases and monitor the development of discommensurations in the near-commensurate regime. Attributing the enhancement of superconducting order to density wave fluctuations, we propose a coupling scheme that yields a phase diagram in qualitative agreement with experiments in conducting transition-metal dichalcogenides. The model predicts the development of nonuniform superconductivity similar to that arising from a pair density wave, with a spatial texture driven by the underlying charge density wave fluctuations.