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

doi:10.1103/PhysRevB.99.115437

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

DOI 10.1103/PhysRevB.99.115437 · Physical Review B

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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∘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 dz2 surface resonance band at the Γ¯ point of the Brillouin zone which 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.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	9.2	Pressure not reported	unknown
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
Pb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	7.2	Pressure not reported	unknown
Re Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	1.7	Pressure not reported	unknown