Superconductivity at 38 K in an electrochemical interface between ionic liquid and Fe(Se0.8Te0.2) on various substrates

TL;DR

This study demonstrates that electrochemical etching in ionic liquid induces a surface superconducting layer in Fe(Se,Te) thin films, achieving 38 K superconductivity regardless of substrate, with properties independent of interface effects.

Contribution

It reveals that electrochemical surface modification can induce high-temperature superconductivity in Fe(Se,Te) films, independent of substrate interface effects.

Findings

Superconductivity at 38 K observed after electrochemical etching.

Surface superconductivity properties are consistent across different substrates.

Superconductivity is attributed to a surface layer formed by electrochemical reaction.

Abstract

Superconducting FeSe0.8Te0.2 thin films on SrTiO3, LaAlO3 and CaF2 substrates were electrochemically etched in an ionic liquid DEME-TFSI electrolyte with a gate bias of 5 V. Superconductivity at 38 K was commonly observed on all substrates after etching the films with a thickness above 30 nm, in spite of different Tc of 8 K, 12 K and 19 K before the etching on SrTiO3, LaAlO3 and CaF2 substrates, respectively. Tc returned to the original value by removing the gate bias. The Tc enhancement on the thick film indicates no relationship between the Tc enhancement and any interface effects between the film and the substrate. The sheet resistance and the Hall coefficient of the surface conducting layer were estimated from the gate bias dependence of the transport properties. The sheet resistance of the surface conducting layer of the films on LaAlO3 and CaF2 showed an identical temperature dependence, and the Hall coefficient is almost temperature independent and -0.05 to -0.2 m2/C, corresponding to 4-17 electrons per one FeSe0.8Te0.2 unit cell area in two dimension. These common transport properties on various substrates suggest that the superconductivity at 38 K appeared in the surface conducting layer produced by electrochemical reaction between the surface of the FeSe0.8Te0.2 thin film and the ionic liquid electrolyte.