Probing enhanced superconductivity in van der Waals polytypes of V$_x$TaS$_2$

TL;DR

This study reveals that inserting insulating layers into TaS$_2$ significantly enhances its superconductivity, with ARPES data showing changes in electronic structure and electron-phonon interactions responsible for the increased $T_c$.

Contribution

The paper introduces a novel vanadium-intercalation method to synthesize TaS$_2$ polytypes, enabling detailed ARPES analysis of layering-dependent superconductivity enhancement.

Findings

Superconducting $T_c$ nearly triples with $1T$ layer insertion.

Charge density wave gap is suppressed in mixed-layer structures.

Electron-phonon coupling increases anisotropically near the Fermi level.

Abstract

Layered transition metal dichalcogenides (TMDs) stabilize in multiple structural forms with profoundly distinct and exotic electronic phases. Interfacing different layer types is a promising route to manipulate TMDs' properties, not only as a means to engineer quantum devices, but also as a route to explore fundamental physics in complex matter. Here we use angle-resolved photoemission (ARPES) to investigate a strong layering-dependent enhancement of superconductivity in TaS$_2$, in which the superconducting transition temperature, $T_c$, of its $2H$ structural phase is nearly tripled when insulating $1T$ layers are inserted into the system. The study is facilitated by a novel vanadium-intercalation approach to synthesizing various TaS$_2$ polytypes, which improves the quality of ARPES data while leaving key aspects of the electronic structure and properties intact. The spectra show the clear opening of the charge density wave gap in the pure $2H$ phase and its suppression when $1T$ layers are introduced to the system. Moreover, in the mixed-layer $4Hb$ system, we observe a strongly momentum-anisotropic increase in electron-phonon coupling near the Fermi level relative to the $2H$ phase. Both phenomena help to account for the increased $T_c$ in mixed $2H$/$1T$ layer structures.