Localization Phenomena in Disordered Tantalum Films

Using dc transport and wide-band spectroscopic ellipsometry techniques we study localization phenomena in highly disordered metallic β -Ta films grown by rf sputtering deposition. The dc transport study implies non-metallic behavior (d ρ /dT < 0), with negative temperature coefficient of resistivity (TCR). We found that as the absolute TCR value increased, specifying an elevated degree of disorder, the free charge carrier Drude response decreases, indicating the enhanced charge carrier localization. Moreover, we found that the pronounced changes occur at the extended spectral range, involving not only the Drude resonance, but also the higher-energy Lorentz bands, in evidence of the attendant electronic correlations. We propose that the charge carrier localization, or delocalization, is accompanied by the pronounced electronic band structure reconstruction due to many-body effects, which may be the key feature for understanding the physics of highly disordered metals

Concurrent bandgap narrowing and polarization enhancement in epitaxial ferroelectric nanofilms

| openaire: EC/FP7/307502/EU//E-CONTROLPeer reviewe

Low-temperature NIR-VUV optical constants of (001) LaAlO3 crystal

Abstract The optical constants and dielectric function of (001) LaAlO3 crystal were investigated at low temperatures down to 10 K in the NIR-VUV spectral range (photon energies 0.8–8.8 eV). Reflection variable angle spectroscopic ellipsometry and transmission spectroscopy were applied. Interband transitions were examined using the Tauc plots and the critical-point analysis. At room temperature, the indirect bandgap of 5.6 ± 0.01 eV and the lowest-energy direct transition at 7.2 ± 0.03 eV were detected. On cooling to 10 K, a blueshift of ∼0.2 eV and ∼0.1 eV was observed for the indirect and direct transitions, respectively. In the transparency spectral range, the index of refraction was found to be nearly temperature-independent and vary with photon energy from 2.0 (1 eV) to 2.5 (5.5 eV). It was suggested that the excellent thermal stability of the index of refraction may be related to the revealed thermally stable interband transitions. The results are of importance for modeling and design of modern optical devices