Evolution of electronic structure in Ca 2−x Sr x RuO 4 observed by photoemission

We report a systematic angle-resolved photoemission study in Ca2−xSrxRuO4 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 t2g orbitals is observed to be similar for all Sr levels, the low-energy quasi- particle (QP) weight changes significantly with x .A txc = 0.5, all the three t2g bands, γ (dxy), α, β (mixing of dyz and dzx) remain metallic, with no major electrontransferamongthem.Thisisincontrasttothescenariooforbital-selective Mott transition proposed to explain the critical behaviour at xc = 0.5. There is a mild change on the γ FS, which changes to hole-like in Ca1.5Sr0.5RuO4 from electron-like in Sr2RuO4. 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.