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 d z 2 surface resonance band at theΓ 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.
SnTe belongs to the recently discovered class of topological crystalline insulators. Here we study the formation of line defects which break crystalline symmetry by strain in thin SnTe films.Strained SnTe(111) films are grown by molecular beam epitaxy on lattice-and thermal expansion coefficient-mismatched CdTe. To analyze the structural properties of the SnTe films we applied in-situ reflection high energy electron diffraction, x-ray reflectometry, high resolution x-ray diffraction, reciprocal space mapping, and scanning tunneling microscopy. This comprehensive analytical approach reveals a twinned structure, tensile strain, bilayer surface steps and dislocation line defects forming a highly ordered dislocation network for thick films with local strains up to 31% breaking the translational crystal symmetry.
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