Fermi-Liquid Versus Pseudogap Behaviors in Filling-Control Transition-Metal Oxides

Abstract

Comparative photoemission studies of Lai1− x Sr x TiO3+y/2 (LSTO) and La2−x Sr x CuO4 (LSCO) have revealed contrasting behaviors in their low-energy electronic properties as the system approaches a filling-control Mott transition from the metallic side. In LSTO and overdoped LSCO, the chemical potential shift, the spectral density of states at the chemical potentialμ and the quasi-particle density atμ can be consistently analyzed within Fermi-liquid theory. In underdoped LSCO, on the other hand, the Fermi-liquid picture breaks down and a relatively wide (~100 meV) pseudogap is opened atμ in the density of states, in addition to a smaller leading-edge shift of ~ 10 meV aroundk ~ (π, 0) in angle-resolved photoemission spectra. The two energy scales increase with decreasing hole concentration x. The larger energy scale is probably associated with antiferromagnetic short-range order while the smaller one is attributed to the spin-gap formation or superconducting fluctuations.