D. Zur

Short-range ordering in beta-YH2+delta and beta-YD2+delta thin films studied by Raman spectroscopy

The metal-insulator transition of Y films grown on (111) CaF 2 substrates and capped with Pd is monitored using Raman spectroscopy. At room temperature the spectra display one Raman active line for cubic YH 2 . 0 and nineRaman active lines for hexagonal YH 3 . For an intermediate hydrogen concentration in YH 2 + δ with δ ≤0.1 a third spectrum is observed, which cannot be explained by a mixture of the border cubic and hexagonal phases. The new spectrum is also observed for an in situ grown YH 2 + δ film, i.e., a sample which was hydrogenated during the growth process of the film. A factor group analysis indicates that this intermediate phase has the I4/mmm structure. Temperature-dependent measurements for these samples point to a short-range ordering of the hydrogen sublattice above 150 K.

Photoemission spectroscopy across the semiconductor-to-metal transition in FeSi

High-resolution angle-resolved photoemission spectroscopy (ARPES) was performed on high-purity FeSi single crystals. Since a high quality of the surface is obligatory to obtain reliably the correct band structure, special care was taken for the in situ preparation. Comparison of the experimental data with band structure calculations in the local density approximation shows that the self-energy resulting from electronic correlation effects leads to a strong renormalization of the energy bands in the vicinity of the Fermi energy. Temperature-dependent ARPES investigations reveal that at elevated temperatures the self-energy is strongly -dependent due to scattering of thermally excited particles and holes near the gap. From the ARPES results, it is obvious that the physical properties of FeSi are due to the high DOS at the edge of the renormalized band gap, but are not determined by a Kondo scenario.