Enhanced Superconductivity and Suppression of Charge-density Wave Order in 2H-TaS$_2$ in the Two-dimensional Limit

TL;DR

This study reveals that reducing the thickness of 2H-TaS2 to the two-dimensional limit significantly enhances its superconducting critical temperature, while suppressing charge-density wave order, due to increased density of states at the Fermi level.

Contribution

It demonstrates the counterintuitive enhancement of superconductivity in 2H-TaS2 as it approaches monolayer thickness, linking electronic structure changes to this phenomenon.

Findings

Superconducting transition temperature increases to 3.4 K in monolayer from 0.8 K in bulk.

Charge-density wave order is suppressed with decreasing thickness.

Electronic structure calculations show increased density of states at the Fermi level.

Abstract

As superconductors are thinned down to the 2D limit, their critical temperature $T_c$ typically decreases. Here we report the opposite behavior, a substantial enhancement of $T_c$ with decreasing thickness, in 2D crystalline superconductor 2H-TaS$_2$. Remarkably, in the monolayer limit, $T_c$ increases to 3.4 K compared to 0.8 K in the bulk. Accompanying this trend in superconductivity, we observe suppression of the charge-density wave (CDW) transition with decreasing thickness. To explain these trends, we perform electronic structure calculations showing that a reduction of the CDW amplitude results in a substantial increase of the density of states at the Fermi energy, which contributes to the enhancement of $T_c$. Our results establish ultra-thin 2H-TaS$_2$ as an ideal platform to study the competition between CDW order and superconductivity.