Emergent Topological Superconductor by Charge Density Wave Transition

TL;DR

This paper demonstrates how charge density wave transitions in monolayer materials can induce topological superconductivity, revealing a new pathway to engineer quantum states through electron doping.

Contribution

It uncovers the emergence of topological superconductivity driven by CDW transitions in monolayer 1H-NbSe$_2$ and 1H-TaSe$_2$, linking electron-phonon interactions to topological phases.

Findings

Coexistence of superconductivity and nontrivial topology in 2x2 CDW phase.

Identification of nonzero Z2 invariant indicating topological order.

Confirmation of similar phenomena in monolayer 1H-TaSe$_2$.

Abstract

Many-body instabilities and topological physics are two attractive topics in condensed matter physics. It is intriguing to explore the interplay between these phenomena in a single quantum material. Here, using the prototypical charge density wave (CDW) material monolayer 1H-NbSe$_2$ as an example, we show how momentum-dependent electron-phonon coupling drives the CDW transition from $3\times3$ to $2\times2$ phase under electron doping. More interestingly, we find the coexistence of superconductivity and nontrivial topology in one of the two $2\times2$ CDW phases, the latter of which is identified by the nonzero Z$_2$ invariant with ideal Dirac cone edge states near the Fermi level. A similar CDW transition-induced topological superconductor has also been confirmed in monolayer 1H-TaSe$_2$. Our findings not only reveal a unique and general method to introduce nontrivial topology by CDW transition, but also provide an ideal platform to modulate different quantum orders by electron doping, thus stimulating experimental interest.