Evolution of electronic structure in Ca 2-xSr xRuO 4 observed by photoemission

Abstract

We report a systematic angle-resolved photoemission study in Ca 2-xSr xRuO 4 for a wide range of Sr concentrations (0.3 ≤ x ≤ 2.0), with a focus on the Fermi surface (FS) topology at x = 0.5, which is believed to be a quantum critical point. While the dispersion of the valence bands formed by the t 2g orbitals is observed to be similar for all Sr levels, the low-energy quasiparticle (QP) weight changes significantly with x. At x c = 0.5, all the three t 2g bands, γ (d xy), α, β (mixing of d yz and d zx) remain metallic, with no major electron transfer among them. This is in contrast to the scenario of orbital-selective Mott transition proposed to explain the critical behaviour at x c = 0.5. There is a mild change on the γ FS, which changes to hole-like in Ca 1.5Sr 0.5RuO 4 from electron-like in Sr 2RuO 4. The doping dependence of the QP weight has a general trend of decreasing with decreasing x, but there is a local maximum at x = 0.5. This suggests that the QP weight is controlled by the competition between Mott localization and disorder-driven localization. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.