Collective charge excitations below the metal-to-insulator transition in BaVS3

The charge response in barium vanadium sulfide (BaVS3) single crystals is characterized by dc resistivity and low-frequency dielectric spectroscopy. A broad relaxation mode in the megahertz range with a huge dielectric constant of approximate to 10(6) emerges at the metal-to-insulator phase transition T-MI approximate to 67 K, weakens with lowering temperature, and eventually levels off below the magnetic transition T-chi approximate to 30 K. The mean relaxation time is thermally activated in a manner similar to the dc resistivity. These features are interpreted as signatures of the collective charge excitations characteristic for the orbital ordering that gradually develops below T-MI and stabilizes at long-range scale below T-chi.