Observation of Two-dimensional Superconductivity in an Ultrathin Iron-Arsenic Superconductor

TL;DR

This study reports the successful fabrication and investigation of ultrathin 2D iron-arsenic superconducting films, revealing intrinsic 2D superconductivity with characteristics distinct from bulk materials.

Contribution

First demonstration of intrinsic 2D superconductivity in ultrathin iron-arsenic superconductor KCa₂Fe₄As₄F₂ with detailed physical characterization.

Findings

Superconductivity observed at 30 K in 2.6-5 nm thick films

Ultrathin films follow the Tinkham model indicating 2D superconductivity

Lower T_c and broader transition compared to bulk material

Abstract

Two-dimensional (2D) superconductors supply important platforms for exploring new quantum physics and high-$T_c$ superconductivity. The intrinsic superconducting properties in the 2D iron-arsenic superconductors are still unknown owing to the difficulties in the preparation of ultrathin samples. Here we report the fabrication and physical investigations of the high quality single-crystalline ultrathin films of the iron-arsenic superconductor KCa$_2$Fe$_4$As$_4$F$_2$. For the sample with the thickness of 2.6$\sim$5 nm (1$\sim$2 unit cells), a sharp superconducting transition at around 30 K (onset point) is observed. Compare with the bulk material, the ultrathin sample reveals a relatively lower $T_c$, wider transition width, and broader flux liquid region under the in-plane field. Moreover, the angle dependent upper critical field follows the Tinkham model, demonstrating the two-dimensional superconductivity in ultrathin KCa$_2$Fe$_4$As$_4$F$_2$.