Tunable critical temperature for superconductivity in FeSe thin films by pulsed laser deposition

Zhongpei Feng,Jun Li,Fang Zhou,Huabing Wang,Dong Li,Kui Jin,Xingyu Jiang,Yulong Huang,Xiaoli Dong,Shunli Ni,Ge He,Beiyi Zhu,Jie Yuan,Wei Hu,Zefeng Lin,Zhongxian Zhao

doi:10.1038/s41598-018-22291-z

Abstract

Stabilized FeSe thin films in ambient pressure with tunable superconducting critical temperature would be a promising candidate for superconducting electronic devices. By carefully controlling the depositions on twelve kinds of substrates using a pulsed laser deposition technique single crystalline FeSe thin films were fabricated. The high quality of the thin films was confirmed by X-ray diffraction with a full width at half maximum of 0.515° in the rocking curve and clear four-fold symmetry in φ-scan. The films have a maximum Tc ~ 15 K on the CaF2 substrate and were stable in ambient conditions air for more than half a year. Slightly tuning the stoichiometry of the FeSe targets, the superconducting critical temperature becomes adjustable below 15 K with quite narrow transition width less than 2 K. These FeSe thin films deposited on different substrates are optimized respectively. The Tc of these optimized films show a relation with the out-of-plane (c-axis) lattice parameter of the FeSe films.

Highlights

The Fe-based superconductors have attracted a lot of attention due to their intriguing superconducting properties and their promise towards novel applications[1,2]
We report on the successful synthesis of a series of high-quality single crystalline superconducting FeSe films on various substrates by pulsed laser deposition (PLD), with a maximum Tc up to 15 K
Since the thickness is considered as a key factor for superconductivity of thin films[22,23,25,29], especially the ultra-thin FeSe system[15,18,29], we studied the thickness dependence of Tc for the FeSe/CF films

Summary

Introduction

The Fe-based superconductors have attracted a lot of attention due to their intriguing superconducting properties and their promise towards novel applications[1,2]. The FeSe bulk crystals exhibit an onset superconducting critical temperature (Tc) of 9 K in ambient pressure[5], which can be enhanced up to 38 K under external pressure. Because of the extreme sensitivity to oxygen, such ultra-thin films of one or a few UC can only be investigated by combining in-situ fabrication and characterization This drastically limits the possibilities to conduct research or develop novel applications based on this intriguing material. The strain, induced by mismatch between the substrate and the film, may play a role in promoting Tc25 It usually takes effect within limited film thickness, plausibly for the ultra-thin FeSe films where the Tc decreases quickly from 1 UC to 3 UC18. Based on abundant high quality and stabilized samples, the relation between the crystal lattice and the tunable Tc has been carefully studied

Methods

Results

Conclusion