Enhanced superconductivity in few-layer TaS$_2$ due to healing by oxygenation

TL;DR

This study demonstrates that oxygenation heals sulfur vacancies in ultrathin TaS2, significantly enhancing its superconducting critical temperature by increasing electron-phonon coupling, revealing defect engineering as a route to improve 2D superconductor performance.

Contribution

The paper shows that oxygenation heals sulfur vacancies in ultrathin TaS2, boosting electron-phonon coupling and superconductivity, which is a novel defect engineering approach for 2D materials.

Findings

Oxygen incorporation is energetically favorable and heals sulfur vacancies.

Enhanced electron-phonon coupling by up to 80% in oxygenated TaS2.

Superconducting critical temperature increases with oxygenation and aging.

Abstract

When approaching the atomically thin limit, defects and disorder play an increasingly important role in the properties of two-dimensional materials. Superconductivity is generally thought to be vulnerable to these effects, but here we demonstrate the contrary in the case of oxygenation of ultrathin tantalum disulfide (TaS$_2$). Our first-principles calculations show that incorporation of oxygen into the TaS$_2$ crystal lattice is energetically favourable and effectively heals sulfur vacancies typically present in these crystals, thus restoring the carrier density to the intrinsic value of TaS$_2$. Strikingly, this leads to a strong enhancement of the electron-phonon coupling, by up to 80% in the highly-oxygenated limit. Using transport measurements on fresh and aged (oxygenated) few-layer TaS$_2$, we found a marked increase of the superconducting critical temperature ($T_{\mathrm{c}}$) upon aging, in agreement with our theory, while concurrent electron microscopy and electron-energy loss spectroscopy confirmed the presence of sulfur vacancies in freshly prepared TaS$_2$ and incorporation of oxygen into the crystal lattice with time. Our work thus reveals the mechanism by which certain atomic-scale defects can be beneficial to superconductivity and opens a new route to engineer $T_{\mathrm{c}}$ in ultrathin materials.