Fabrication and characterization of scanning tunneling microscopy superconducting Nb tips having highly enhanced critical fields
A. Kohen, Y. Noat, T. Proslier, E. Lacaze, M. Aprili, W. Sacks, D., Roditchev
TL;DR
This paper presents a simple in-situ fabrication method for superconducting niobium tips used in scanning tunneling microscopy, achieving atomic resolution and significantly enhanced critical magnetic fields due to size effects.
Contribution
The study introduces a straightforward technique to produce Nb superconducting tips with enhanced critical fields, matching bulk properties and enabling improved STM measurements.
Findings
Superconducting Nb tips show a critical temperature of 9.2 K.
Critical magnetic field of tips is up to five times larger than bulk Nb.
Tips achieve atomic resolution in STM imaging.
Abstract
We report a simple method for the fabrication of Niobium superconducting (SC) tips for scanning tunnelling microscopy which allow atomic resolution. The tips, formed in-situ by the mechanical breaking of a niobium wire, reveal a clear SC gap of 1.5 meV and a critical temperature Tc=9.2+-0.3 K as deduced from Superconductor Insulator Normal metal (NIS) and Superconductor Insulator Superconductor (SIS) spectra. These match the values of bulk Nb samples. We systematically find an enhanced value of the critical magnetic field in which superconductivity in the tip is destroyed (around 1 T for some tips) up to five times larger than the critical field of bulk Nb (0.21 T). Such enhancement is attributed to a size effect at the tip apex
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