The outstanding discrepancy between the measured and calculated (local-density approximation) Fermi surfaces in the well-characterized, paramagnetic Fermi liquid Sr2RhO4 is resolved by including the spin-orbit coupling and Coulomb repulsion. This results in an effective spin-orbit coupling constant enhanced 2.15 times over the bare value. A simple formalism allows discussion of other systems. For Sr2RhO4, the experimental specific-heat and mass enhancements are found to be 2.2.PACS numbers: 71.18.+y, 71.20.-b, 71.30.+h Since the discoveries of high-temperature superconductivity and colossal magnetoresistance in Mott insulators made metallic by hole-doping, transition-metal oxides have remained at the forefront of research. Their many lattice and electronic (orbital, charge, and spin) degrees of freedom are coupled by effective interactions (electron-phonon, hopping, t, Coulomb repulsion, U, and Hunds-rule coupling, J), and when some of these are of similar magnitude, competing phases may exist in the region of controllable compositions, fields, and temperatures. The interactions tend to remove low-energy degrees of freedom, e.g. to reduce the metallicity. This rarely happens by merely shifting spectral weight from a quasiparticle band into incoherent Hubbard bands, as in the U/t-driven metal-insulator transition for the single-band Hubbard model, but is usually assisted by lattice distortions which break the degeneracy of lowenergy orbitals and split the corresponding quasiparticle -or partly incoherent-bands away from the chemical potential. According to recent calculations using the local density-functional plus dynamical mean-field approximation (LDA+DMFT), such Coulomb-enhanced crystal-field splitting seems to be the mechanism triggering the expansion-induced metal-insulator transition in undoped LaMnO 3 [1] and in V 2 O 3 [2], long considered the prototype Mott transition. The low-temperature, antiferromagnetically-ordered, insulating phase of V 2 O 3 is well described [3] in the LDA+U static mean-field approximation, which yields the configuration t . Although this approximation exaggerates the tendency towards symmetry breaking, it does give a reasonable description of the shape of the Fermi surface (FS) on the metallic side of the transition [1,2].When going from 3d to 4d transition-metal oxides, the larger extent of the 4d orbitals cause the hopping, t, and the coupling to the lattice to increase, and U and J to decrease. This is reflected in the rich electronic properties of e.g. the t 4 2g ruthenates in the Ruddlesden-Popper series (Ca 1−x Sr x ) ν+1 Ru ν O 3ν+1 [4,5,6,7,8]. Here, the end-members (ν=1 and ν=∞) have the same structures as respectively La 2 CuO 4 (2D K 2 NiF 4 -type) and LaMnO 3 (3D perovskite). The relatively small size and strong covalency of the Ca ions cause the RuO 6 octahedra to rotate and tilt. The resulting misalignment of the Ru t 2g Wannier orbitals (WOs) reduces the hopping between them, and so does the deformation of the WOs caused by Ca-O-t 2g covalency [9,10]. As a resu...
The wave-vector (q) and doping (x, y) dependences of the magnetic energy, iron moment, and effective exchange interactions in LaFeAsO1−xFx and Ba1−2yK2yFe2As2 are studied by self-consistent LSDA calculations for co-planar spin spirals. For the undoped compounds (x = 0, y = 0), the minimum of the calculated total energy, E(q), is for q corresponding to stripe antiferromagnetic order. Already at low levels of electron doping (x), this minimum becomes flat in LaFeAsO1−xFx and for x 5%, it shifts to an incommensurate q. In Ba1−2yK2yFe2As2, stripe order remains stable for hole doping up to y = 0.3. These results are explained in terms of the band structure. The magnetic interactions cannot be accurately described by a simple classical Heisenberg model and the effective exchange interactions fitted to E(q) depend strongly on doping. The doping dependence of the E(q) curves is compared with that of the noninteracting magnetic susceptibility for which similar trends are found.PACS numbers: 75.25.+z, 75.30.Fv
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