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

TL;DR

This paper develops a theoretical framework to understand how discommensurations in charge density waves can enhance superconductivity in transition-metal dichalcogenides, aligning with experimental observations.

Contribution

It introduces a McMillan-Ginzburg-Landau model that captures the competition and coexistence of charge-density and superconducting orders, including discommensurations.

Findings

Phase diagram consistent with experiments

Prediction of non-uniform superconductivity driven by charge fluctuations

Identification of discommensurations as a mechanism for superconductivity enhancement

Abstract

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 non-uniform superconductivity similar to that arising from a pair-density wave, with a spatial texture driven by the underlying charge-density wave fluctuations.