Softening of Cu-O Bond Stretching Phonons in TetragonalHgBa2CuO4+δ

Abstract

Phonons in nearly optimally doped HgBa(2)CuO(4+delta) were studied by inelastic x-ray scattering. The dispersion of the low-energy modes is well described by a shell model, while the Cu-O bond stretching mode at high energy shows strong softening towards the zone boundary, which deviates strongly from the model. This seems to be common in the hole-doped high-T(c) superconducting cuprates, and, based on this work, not related to a lattice distortion specific to each material.

Hard-Wired Dopant Networks and the Prediction of High Transition Temperatures in Ceramic Superconductors

“…Again decades of research on network glasses have shown that the best weighting is the simplest, that is, equal weighting ( R ) for all atoms Advances in Condensed Matter Physics 5 provides the best description of glass-forming ability and the glass transition, because the overall network is mechanically marginally stable (MMS). As discussed earlier, shell-model calculations [31] of phonon spectra in HTSC are generally unable to predict very soft modes, especially those associated with dopants. Quite revealing is the fact that the fitted effective charges for "soft layer" rare earth cations in shell models of LSCO and YBCO phonon spectra derived from neutron scattering were inexplicably negative [32].…”

Softening of bond-stretching phonon mode in Ba1−xKxBiOKhosroabadi1, Miyasaka2, Kobayashi3 et al. 2011Phys. Rev. BSelf Cite

“…By contrast, in the high-T c superconducting cuprates (HTSCs), the phonon contribution to superconductivity remains unclear, although the high-frequency oxygen mode (Cu-O bond stretching mode) shows strong softening as the momentum transfer is changed [10][11][12][13][14][15][16][17] . The main subject of discussion for the cuprates is the rapid drop of the bond stretching phonon frequency, and increased in linewidth, in the (q, 0, 0) direction at q > 0.25, which is not reproduced by the LDA calculations 14,18,19 .…”

Lattice dynamics and electron-phonon coupling inSr2RuO4: Inelastic neutron scattering and shell-model calculations

“…The lattice dynamics in Sr 2 RuO 4 merits further interest as a reference material for the large class of transition metal-oxides with a perovskite related structure where an anomalous phonon dispersion has been observed [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. Stimulated by the phenomenon of high-temperature superconductivity the phonon dispersion of many oxide perovskites has been studied in detail.…”

“…In particular in the insulating parent compounds, like La 2 CuO 4 , all features in the phonon dispersion are at least qualitatively described by simple ionic models. In electronically doped materials, like (La, Sr) 2 CuO 4 , however, significant discrepancies in the dispersion of the longitudinal bond-stretching branches were discovered [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. A typical lattice dynamical model including an isotropic screening function will always predict an increasing bondstretching dispersion when passing from the Brillouinzone center into the zone due to the imperfect screening of the Coulomb-potentials at short distance.…”

“…A typical lattice dynamical model including an isotropic screening function will always predict an increasing bondstretching dispersion when passing from the Brillouinzone center into the zone due to the imperfect screening of the Coulomb-potentials at short distance. Instead a decreasing dispersion with the longitudinal zone-boundary frequencies falling below those of the transverse branch has been observed in numerous perovskite materials : in different types of superconducting cuprates [6,7,8,9,10,11,12,13,14,15], in nickelates [16,17], in manganates [18] and in superconducting Ba 1−x K x BiO 3 [19,20,21], for a recent review of these effects see reference [15]. These doping-induced effects are frequently called overscreening [24] referring to the fact that simple screening should soften the longitudinal phonon modes.…”