Doctor of Philosophy (PhD)


Physics and Astronomy

Document Type



LaSb2 has recently been found to have unusual magnetoresistive properties despite the fact that neither La nor Sb are magnetic. The resistance is anisotropic, and at high magnetic fields presents an anomaly that might be a result of a charge density transition. The magnetoresistance is anisotropic and linear, and the resistivity presents high relative changes when a magnetic field is applied. Discovered in 1954, LaSb2, as the rest of the light rare-earth diantimonides, was poorly studied. The anisotropic magnetic properties reported in 1998 by Bud'ko, Canfield and their collaborators make the series very interesting. A description of the electronic structure and Fermi surface topology would be of great help in understanding the properties exhibited by LaSb2, and the rest of the diantimonides. Single-crystals of LaSb2 were grown by metallic flux method using high-purity La and Sb. Single-crystal X-ray diffraction measurements confirmed the SmSb2 orthorhombic structure with a=6.38 b=6.23 and c=18.75Å. LaSb2 presents a micaceous structure, with layers of Sb separated by bi-layers of La-Sb chains. X-ray measurements revealed a mosaic spread of ~0.5-1° and it is likely that the material is highly twinned. After the material is cleaved in vacuo, STM measurements give flat terraces separated by half unit-cell step edges. High-resolution angle-resolved photoemission spectroscopy has been performed on LaSb2 to study the electronic band structure near the Fermi level and provide information to the Fermi surface topology. Photoemission studies show that the electronic structure is highly two-dimensional, and the locations of the critical points Γ and Z in band dispersion are identified. Neutron diffraction reveals doublet structures as a result of the crystal twinning. At low temperature, new spots are identified, indicating two new substructures that are incommensurate with the main lattice. The reduced dimensionality of the system, the nested Fermi surfaces, and the new periodicities that develop at low temperature can be reconciled in a model characterized by strong electron-phonon coupling that result in a charge-density wave due to an associated Peierls instability and a lattice distortion.



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Committee Chair

Richard L. Kurtz