Andreev reflection measurements in nanostructures with amorphous WC$_x$ superconducting contacts

TL;DR

This study demonstrates the use of focused ion beam-grown amorphous WC$_x$ superconducting tips for point-contact Andreev reflection spectroscopy on nanostructures, analyzing conductance curves with Blonder-Tinkham-Klapwijk theory.

Contribution

It introduces a novel method of fabricating superconducting tips via FIB for nanoscale spectroscopy and evaluates their effectiveness in point-contact measurements.

Findings

Clear signatures of Andreev reflection observed in conductance measurements.

FIB-produced WC$_x$ tips enable detailed spectroscopy of metallic nanostructures.

Analysis aligns with Blonder-Tinkham-Klapwijk theory, confirming the method's validity.

Abstract

Point-contact Andreev reflection measurements of Co/ and Cu/tungsten-carbide (WC$_x$) contacts are presented. Metallic thin films were patterned by e-beam-lithography and lift-off; tungsten carbide superconducting tips were grown directly on the pre-patterned samples by decomposition of a metallo-organic vapour (tungsten hexacarbonyl) under a focused Ga$^+$-ion beam (FIB). Current-voltage measurements as a function of temperature and magnetic field clearly showed the signatures of Andreev reflection. The experimental conductance-voltage curves were analyzed within the Blonder-Tinkham-Klapwijk theory. The results highlight the possibilities, advantages and disadvantages of using FIB-produced amorphous WC$_x$ tips for point-contact spectroscopy in metallic nanostructures.