Josephson Effect in Pb/I/NbSe2 Scanning Tunneling Microscope Junctions

TL;DR

This paper presents a method for fabricating superconducting STM tips to study Josephson effects in superconductor/insulator/superconductor junctions, revealing insights into NbSe2's superconductivity and charge density wave interactions.

Contribution

It introduces a reproducible fabrication technique for superconducting STM tips and demonstrates their use in probing Josephson effects in NbSe2.

Findings

Observation of fluctuation dominated Josephson effects.

Lower than expected IcRn in NbSe2 due to charge density wave interactions.

Method for inferring IcRn from tunneling characteristics.

Abstract

We have developed a method for the reproducible fabrication of superconducting scanning tunneling microscope (STM) tips. We use these tips to form superconductor/insulator/superconductor tunnel junctions with the STM tip as one of the electrodes. We show that such junctions exhibit fluctuation dominated Josephson effects, and describe how the Josephson product IcRn can be inferred from the junctions' tunneling characteristics in this regime. This is first demonstrated for tunneling into Pb films, and then applied in studies of single crystals of NbSe2. We find that in NbSe2, IcRn is lower than expected, which could be attributed to the interplay between superconductivity and the coexisting charge density wave in this material.