Pseudogap formation in 4d transition metal oxide BaRuO3

Optical spectra of nine-layer BaRuO3 show clear electrodynamic response cha nges due to a pseudogap formation. As temperature decreases, the pseudogap formation induces a gradual reduction of carrier density n and an abrupt su ppression of scattering rate 1/tau. It was found that the competition betwe en n and 1/tau can induce a crossover from metallic to insulator-like regio ns. A clear development of the pseudogap as well as the coherent component in BaRuO3 is evidently distinguished from other pseudogap phenomena observe d in high T-c cuprates and heavy-electron systems.