Layer thickness and substrate effects on superconductivity in epitaxial FeSe films on BLG/SiC(0001)

TL;DR

This study investigates how substrate choice and layer thickness influence superconductivity in FeSe films on bilayer graphene, revealing suppression in ultrathin films and emergence at greater thicknesses, highlighting substrate effects on 2D superconductivity.

Contribution

It provides detailed structural and electronic characterization of FeSe on BLG/SiC(0001), demonstrating substrate-dependent superconductivity development in ultrathin films.

Findings

Ultrathin FeSe on BLG/SiC(0001) is metallic but not superconducting.

Superconductivity appears in thicker FeSe films with a Tc of 6 K.

Substrate effects significantly influence superconductivity in 2D FeSe.

Abstract

The layered nature and simple structure of FeSe reveal this iron-based superconductor as a unique building block for the design of artificial heterostructure materials. While superconductivity develops in ultrathin films of FeSe on SrTiO3 substrates, it remains unclear whether it can be developed on more chemically inert, layered materials such as graphene. Here, we report on the characterization of the structural, chemical and electronic properties of few-layer FeSe on bilayer graphene grown on SiC(0001) using low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) and X-ray photoelectron spectroscopy (XPS). STM imaging of our FeSe films with thicknesses up to three layers exhibit the tetragonal crystal structure of bulk FeSe, which is supported by XPS spectra consistent with the FeSe bulk counterpart. While our STS measurements at 340 mK reveal a metallic character for few-layer FeSe on BLG/SiC(0001), they show an absence of superconductivity, as the low-lying electronic structure exhibits a spatially anisotropic dip-like feature robust against magnetic fields. Superconductivity in FeSe/BLG/SiC(0001), however, emerges for thicker films with a transition temperature of 6 K. Our results underscore the significance of the substrate as key factor driving the suppression superconductivity in FeSe in the 2D limit.