Layered Ruthenium Oxides: From Band Metal to Mott Insulator

Abstract

We present results of the first optical and angle-resolved photoemission study on a layered ruthenium oxide system with various Ca͞Sr substitution levels. Using two-plane ͑Sr 12x Ca x ͒ 3 Ru 2 O 7 and one-plane Ca 2 RuO 4 crystals we were able to study evolution of the electronic properties in a range from a band metal ͑Sr 3 Ru 2 O 7 ͒ to a "bad" metal ͑Ca 3 Ru 2 O 7 ͒ to a Mott-Hubbard insulator ͑Ca 2 RuO 4 ͒. Apart from a Mott-Hubbard metal-insulator transition (MIT), we have uncovered a qualitative change of the electronic properties at a critical x 0.33. We suggest that the latter is a result of a quantum phase transition into an antiferromagnetic phase that precedes the real Mott-Hubbard MIT. [S0031-9007(98)07196-8]

Crystal structure and electronic and magnetic properties of the bilayered rhodium oxideSr3Rh2OYamaura1, Huang2, Young3 et al. 2002Phys. Rev. B313360View full textAdd to dashboardCite

“…8,9,10,11,12 Finally, data suggest that a quantum critical point exists in the solid solution Sr 1−x Ca x RuO 3 for x ∼0.7 between ferromagnetic (Sr-side) and nearly ferromagnetic (Ca-side) ordered states. 13,14,15,16,17,18 These materials have provided experimental opportunities to study criticality of correlated electrons in the vicinity of the quantum critical points.…”

Destruction of the Mott insulating ground state ofCa2RuO4by a structural transition

“…Based on these studies, a few major features are known [3,8,9] : (1) It has the K 2 NiF 4 structure with large rotations and tilts of the RuO 6 octahedra compared to Sr 2 RuO 4 and due to the smaller ionic radius of Ca; (2) it appears to be a Mott insulator below T=300 K with a narrow gap of about 0.2 eV, as determined from both transport and optical measurements [10] ; (3) it is antiferromagnetically ordered below T N =110 K; and (4) the magnetic moment (≈0.4 µ B /Ru at 30 T) is low compared to the other Ca-and Sr-ruthenates [3] which have moments closer to the 2.0 µ B /Ru expected for the low spin (S=1) state of the Ru 4+ (4d 4 ) configuration.…”

Ferromagnetic transition in the correlated4dperovskitesSrRu1−xRhYamaura1, Young2, Takayama‐Muromachi3 2004Phys. Rev. B253210View full textAdd to dashboardCite

“…Perovskite-ruthenium oxides and the single-structure family form a distinguished class of the 4d-band oxides that show rich electronic phenomena, such as unconventional superconductivity, 1,2 a quantum critical transition, 3,4,5,6,7 and negative spin polarization. 8 These phenomena are of great interest to the condensed matter community, and thus, these materials have recently received much attention.…”