Investigation of TiO$_x$ barriers for their use in hybrid Josephson and tunnelling junctions based on Ba-122 thin films

TL;DR

This study explores oxidized titanium layers as barriers in hybrid Josephson and tunneling junctions, demonstrating tunable behavior from Josephson to tunnel-like, with promising results on BaFe$_2$As$_2$ thin films for superconducting applications.

Contribution

It introduces a method to control junction behavior using TiO$_x$ barriers in BaFe$_2$As$_2$ based junctions, enabling high $I_cR_n$ products and tunable transport mechanisms.

Findings

Clear Josephson effects with $I_cR_n$ $ oughly$ 90 $$V at 4.2 K for 1.5 nm barriers.

Transition from Josephson to tunnel-like behavior with increasing barrier thickness.

Junctions exhibit SNS'-like transport dominated by Andreev reflection at optimal thickness.

Abstract

We tested oxidized titanium layers as barriers for hybrid Josephson junctions with high $I_cR_n$-products and for the preparation of junctions for tunneling spectroscopy. For that we firstly prepared junctions with conventional superconductor electrodes lead and niobium, respectively. By tuning the barrier thickness we were able to change the junctions' behavior from a Josephson junction to tunnel-like behavior applicable for quasi-particle spectroscopy. Subsequently, we transferred the technology to junctions using Co-doped BaFe$_2$As$_2$ thin films prepared by pulsed laser deposition as base electrode and evaporated Pb as counter electrode. For barriers with a thickness of 1.5\,nm we observe clear Josephson effects with $I_cR_n$\,$\approx$\,90\,$\mu$V at 4.2\,K. These junctions behave SNS'-like and are dominated by Andreev reflection transport mechanism. For junctions with barrier thickness of 2.0\,nm and higher no Josephson but SIS'- or SINS'-like behavior with a tunnel-like conductance spectrum was observed.