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arXiv · 1906.07796

On the preparation and electronic properties of clean superconducting Nb(110) surfaces

Artem B. Odobesko·Soumyajyoti Haldar·Stefan Wilfert·Jakob Hagen·Johannes Jung·Niclas Schmidt·Paolo Sessi·Matthias Vogt·Stefan Heinze·Matthias Bode
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Abstract

We have studied cleaning procedures of Nb(110) by verifying the surface quality with low-energy electron diffraction, Auger electron spectroscopy, and scanning tunneling microscopy and spectroscopy. Our results show that the formation of a surface-near impurity depletion zone is inhibited by the very high diffusivity of oxygen in the Nb host crystal which kicks in at annealing temperatures as low as a few hundred degree Celsius. Oxygen can be removed from the surface by heating the crystal up to $T = 2400^\circ$C. Tunneling spectra measured on the clean Nb(110) surface exhibit a sharp conductance peak in the occupied states at an energy of about $-450$\,meV. Density functional theory calculations show that this peak is caused by a $d_{z^2}$ surface resonance band at the $\bar{\Gamma}$ point of the Brillouin zonewhich provides a large density of states above the sample surface. The clean Nb(110) surface is superconducting with a gap width and a critical magnetic field strength in good agreement to the bulk value. In an external magnetic field we observe the Abrikosov lattice of flux quanta (vortices). Spatially resolved spectra show a zero-bias anomaly in the vortex core.

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Artem B. Odobesko, Soumyajyoti Haldar, Stefan Wilfert, Jakob Hagen, Johannes Jung, Niclas Schmidt, Paolo Sessi, Matthias Vogt, Stefan Heinze, Matthias Bode. 2019-06-18. On the preparation and electronic properties of clean superconducting Nb(110) surfaces. https://doi.org/10.1103/physrevb.99.115437

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