Dynamic properties of inhomogeneous states in cuprates (Review Article)

Abstract

We review the static and dynamical properties of stripe textures with regard to their relevance in high-T c superconductors. Our investigations are based on the time-dependent Gutzwiller approximation which allows for the computation of random-phase approximation-like (RPA) fluctuations on top of the Gutzwiller approximation (GA). No restrictions are imposed on the charge and spin configurations which makes the method suitable for the calculation of linear excitations around symmetry-broken solutions. Within this approach we calculate the optical conductivity of stripes and compare our results with reflectivity experiments on cuprates. Furtheron we use the spin-rotational invariant extension of the GA + RPA method in order to investigate the characteristics of magnetic excitations in the stripe phase of cuprates. Our results are in very good agreement with neutron scattering and optical experiments on lanthanum cuprate superconductors.

Small polarons and magnetic antiphase boundaries inCa2−xNaxCuO2ClPatterson1 2008Phys. Rev. B18090View full textAdd to dashboardCite

“…10͒ and model Hamiltonian calculations. 16 The schematic diagram in the top panel of Fig. 6 shows blocks of antiferromagnetically ordered copper spins separated by magnetic APB containing polaronic oxygen ions and ferromagnetically ordered copper spins.…”

“…25 Further experimental evidence for polaronic states in cuprates is provided by the observation of strong electronphonon coupling: Very broad, Gaussian photoemission line shapes are widely observed in cuprates and attributed to Franck-Condon broadening; 3,6 pinning of charge carriers by a crystallographic distortion in a low temperature tetragonal phase of La 2−x Ba x CuO 4 ͑LBCO͒, with 0.11Ͻ x Ͻ 0.14, can be lifted and superconductivity restored by application of hydrostatic pressure; 1 new features in the midinfrared optical absorption spectrum of doped transition metal oxides, including cuprates, 32,33 were attributed to polarons and modeled using a model Hamiltonian approach. 16 A phonon anomaly was observed in LBCO ͑x = 0.12͒ at a wave vector, which corresponds to the 4a 0 stripe spacing. 34 a 0 is the lattice constant in CuO 2 planes.…”

“…11 These observations are in sharp contrast to density functional theory studies which omit a Hubbard U term, in which case the antiferromagnetic, insulating parent compound is usually predicted to be metallic. 14,15 An extensive model Hamiltonian study of striped phases of cuprates found linear chains of holes in a half-filled stripe state 16 and the formation of charged lines of holes on oxygen ions in CuO 2 planes was predicted using Hubbard models. [17][18][19] A hybrid density functional approach, 20,21 which includes Hartree-Fock exchange with a weighting factor, is used to study hole states in Ca 2−x Na x CuO 2 Cl 2 ͑Na-CCOC͒, with x = 0.0625 and 0.125 in this work; inclusion of Hartree-Fock exchange in the Hamiltonian leads to a polaronic description of hole states in cuprates and other oxides 8,9,22 and correctly predicts an antiferromagnetic insulating state for the parent compound of the doped cuprates studied here.…”