Thickness dependence of superconductivity in FeSe films

TL;DR

This study investigates how the number of layers in FeSe films influences their superconducting properties, using theoretical models to explain experimental observations and highlighting the role of electronic correlations.

Contribution

The paper combines DFT analysis and BCS theory to elucidate the thickness dependence of superconductivity in FeSe films, emphasizing correlation effects independent of substrates.

Findings

Superconducting Tc varies with film thickness from 1 to 5 layers.

Correlation effects are crucial for understanding superconductivity in FeSe films.

Theoretical Tc estimates align with experimental data.

Abstract

The films of FeSe on substrates have attracted attention because of their unusually high-temperature (Tc) superconducting properties whose origins continue to be debated. To disentangle the competing effects of the substrate and interlayer and intralayer processes, we present here results of density functional theory (DFT)-based analysis of the electronic structure of unsupported FeSe films consisting of 1 to 5 layers (1L-5L). Furthermore, by solving the Bardeen-Schrieffer-Cooper (BCS) equation with spin-wave exchange attraction derived from the Hubbard model, we find the superconducting critical temperature Tc for 1L-5L and bulk FeSe systems in reasonable agreement with experimental data. Our results point to the importance of correlation effects in superconducting properties of single- and multi-layer FeSe films, independently of the role of substrate.