Terahertz time-domain spectroscopy has emerged as a powerful tool to investigate correlated electron materials where the interplay between microscopic degrees of freedom leads to phenomena such as superconductivity or metal-insulator transitions. I will discuss our recent results with emphasis on two well-known vanadates: VO 2 and V 2 O 3 .
The nascent field of photoinduced phase transitions utilizes time-resolved optical spectroscopy to initiate a cooperative response in a given material with a view towards creating new macroscopically ordered phases. Various correlated electron materials are under active investigation in this regard given their well-known sensitivity to external perturbations. We have been investigating V 2 O 3 which undergoes a transition from antiferromagnetic insulator at low temperatures to a strongly correlated metal above ~160K. Optical-pump THz-probe studies on V 2 O 3 thin films reveal coherent oscillations in the far-infrared conductivity. The 100 ps conductivity oscillations result from optically induced strain and are suggestive of an induced decrease of the electronic bandwidth thereby driving V 2 O 3 from the correlated metallic state towards a paramagnetic insulating phase.
I will also present our very recent studies of epitaxial VO 2 thin films grown on TiO 2 substrates. The conductivity of these films approaches that of high quality single crystals. Of particular interest is the potential to control the metal-insulator transition through substrate induced strain.