Scanning Tunneling Spectroscopy of Rare Earth Hexaborides
von Philipp Buchsteiner
Datum der mündl. Prüfung:2020-09-25
Betreuer:Dr. Martin Wenderoth
Gutachter:Dr. Martin Wenderoth
Gutachter:Prof. Dr. Stefan Mathias
EnglischRare earth hexaborides are a well-suited model system for the exploration of correlation physics. The varying 4f occupation of the rare earth elements result in a richness of correlated electron phenomena, which harbor both, an ideal playground for fundamental science and an immense potential for technological applications. Especially the surface physics of hexaborides has gained special attention due to fact that lanthanum hexaboride (LaB6) is commonly in use as electron emitter, because of the surprisingly low work function of the (001) surface. However, a thorough understanding of the atomic and electronic structure of hexaboride surfaces is still missing. In this thesis, the (001) cleavage planes of LaB6 and PrB6 are investigated by complementary experimental and theoretical techniques. Using scanning tunneling microscopy and low-energy electron diffraction a chainlike (2x1) reconstruction is found on the LaB6 (001) cleavage plane, apart from a widely disordered surface. Density functional theory (DFT) resolves this reconstruction as La chains on a B6 layer. Scanning tunneling spectroscopy reveals a peak in the differential conductance below the Fermi energy, which is, as determined by DFT slab calculations, a boron dangling bond feature, which is hybridized with La d-states. On the PrB6 (001) cleavage plane a chainlike (2x1) reconstruction is found, too, as well as two uniform terminations. The uniform terminations are assigned as complete Pr or B6 layers. The Pr termination and the chainlike (2x1) reconstruction show a peak in the differential conductance at -0.7 eV and at -1.1 eV, respectively, which are tentatively associated with 4f-related states.
Keywords: rare earth hexaborides; scanning tunneling microscopy; scanning tunneling spectroscopy; local density of states; surface states; surface reconstruction; electronic structure; dangling bonds; 4f electrons; low-energy electron diffraction; density functional theory; gamma ray diffraction