Seminars Archive

Polarization resolved infrared spectroscopy study of the electrodynamic properties of vanadium dioxide thin films and single crystals undergoing an insulator-to-metal transition.

Abstract
anadium dioxide (VO2) is one of the best known transition metal oxides, presenting a rich phase diagram. In the monoclinic phase vanadium-vanadium dimers form and the solid has an energy gap in the near-infrared. Above the critical temperature of the insulator-to-metal transition (IMT) dimers break and VO2 shows tetragonal symmetry and no gap. The issue is whether the nature of the low temperature state is mainly due to the strong electronic correlation (Mott-Hubbard insulator) or to the structural distortion (Peierls band insulator). The focus of the present work is to evaluate the vibrational and electronic response of titanium doped VO2 single crystals and VO2 thin films along the main crystallographic directions. The spectroscopic analysis has been performed with linearly polarized radiation with frequencies going from the far-infrared to the ultraviolet frequencies, allowing to obtain the frequency dependent optical conductivity and the phononic spectrum of the samples for each polarization and as functions of titanium doping and film thickness. It has also been observed that the optical conductivity of free carriers, in the direction of the dimers, jumps of four orders of magnitude in single crystals with a 5.9% titanium content and of three orders of magnitude in thin films.