High-temperature superconductivity and its robustness against magnetic polarization in monolayer FeSe on EuTiO3

Chong Liu,Giorgio Levy,Hsiang-Hsi Kung,Andrin Doll,Ryan P Day,Ke Zou,Jan Dreiser,Andrea Damascelli,Hyungki Shin,Bruce A Davidson,Cinthia Piamonteze

doi:10.1038/s41535-021-00388-5

Abstract

Spin degree of freedom generally plays an important role in unconventional superconductivity. In many of the iron-based compounds, superconductivity is found in close proximity to long-range antiferromagnetic order, whereas monolayer FeSe grown on SrTiO3, with enhanced superconductivity, exhibits no magnetic or nematic ordering. Here we grow monolayer and multilayer FeSe on antiferromagnetic EuTiO3(001) layers, in an effort to introduce a spin polarization in proximity to the superconductivity of FeSe. By X-ray magnetic dichroism, we observe an antiferromagnet–ferromagnet switching on Eu and Ti sites in EuTiO3 driven by the applied magnetic field, with no concomitant spin polarization on the Fe site of FeSe. Transport measurements show enhanced superconductivity of monolayer FeSe on EuTiO3 with a transition temperature of ~30 K. The band structure revealed by photoemission spectroscopy is analogous to that of FeSe/SrTiO3. Our work creates a platform for the interplay of spin and unconventional superconductivity in the two-dimensional limit.

Highlights

Spin degree of freedom generally plays an important role in unconventional superconductivity
We study the epitaxial interface between a 2D high-temperature superconductor—monolayer FeSe—and an antiferromagnetic (AFM) insulator—EuTiO3 (ETO), which allows direct access to study and control the properties through all the standard techniques suitable for 2D materials
Undoped bulk FeSe is superconducting below 8 K11, above which only nematicity but no long-range magnetic order is present at ambient pressure[12,13,14], strong spin fluctuations have been found by inelastic neutron scattering[15]

Summary

Introduction

Spin degree of freedom generally plays an important role in unconventional superconductivity. In many of the iron-based compounds, superconductivity is found in close proximity to long-range antiferromagnetic order, whereas monolayer FeSe grown on SrTiO3, with enhanced superconductivity, exhibits no magnetic or nematic ordering. Spintronics[1] offers the potential for creating circuits in which logic operations controlled by spin currents are faster and more energetically efficient than equivalent charge-based semiconductor devices. It requires control of spin and charge at the nanoscale, allowing devices with a greater diversity of functionality. Two-dimensional (2D) materials that are only a few atomiclayers thick serve as a potential platform to combine superconductivity and magnetism To date, their coexistence in the 2D limit has been discovered in LaAlO3/SrTiO35–8 and LaAlO3/EuTiO3/ SrTiO3 interfaces[9]. Magnetic exchangebias measurements found evidences of antiferromagnetic order in as-grown FeSe thin films on STO; upon annealing, the sample became superconducting and AFM order disappeared[44]

Methods

Results

Conclusion