Interface-induced superconductivity and strain-dependent spin density wave in FeSe/SrTiO3 thin films

TL;DR

This study reveals how interface effects and strain influence superconductivity and spin density waves in FeSe/SrTiO3 thin films, providing insights into enhancing Tc in iron-based high-temperature superconductors.

Contribution

It demonstrates the role of substrate-induced electron transfer and strain in suppressing spin density waves, leading to superconductivity in FeSe films, and establishes a comprehensive phase diagram.

Findings

Superconductivity in FeSe is enhanced by substrate-induced electron transfer.

Spin density wave presence weakens with increased film thickness or reduced strain.

A phase diagram of FeSe vs. lattice constant is established, capturing key physics of Fe-HTS.

Abstract

The record of superconducting transition temperature(Tc) has long been 56K for the iron-based high temperature superconductors(Fe-HTS's). Recently, in single layer FeSe films grown on SrTiO3 substrate, signs for a new 65K Tc record are reported. Here with in-situ photoemission measurements, we substantiate the presence of the spin density wave(SDW) in FeSe films, a key ingredient of Fe-HTS that was missed in FeSe before, which weakens with increased thickness or reduced strain. We demonstrate that the superconductivity occurs when the electrons transferred from the oxygen-vacant substrate suppress the otherwise most pronounced SDW in single layer FeSe. Besides providing a comprehensive understanding of FeSe films and directions to further enhance its Tc, we establish the phase diagram of FeSe vs. lattice constant that contains all the essential physics of Fe-HTS's. With the simplest structure, cleanest composition and single tuning parameter, it is ideal for testing theories of Fe-HTS's.