Screening and Phonon-Plasmon Scenario as Calculated from a Realistic Electronic Bandstructure Based on LDA for La2CuO4

Abstract

The investigations performed in this work primarily deal with the question whether or no phonon±plasmon coupling along the c-axis in metallic La 2 CuO 4 will occur in case a realistic electronic bandstructure based on the local density approximation (LDA) is employed for the calculation of the electronic polarizability P and the dielectric matrix e. Phonon±plasmon mixing will appear in a significant way if the frequency of the free, uncoupled plasmon, as determined from the zeros of the dielectric matrix e, will fall into the frequency range of the phonon modes of appropriate symmetry coupling to the plasmon. For such a possibility to arise the dispersion of the electronic bandstructure along the c-axis must be sufficiently weak (small bandwidth). Qualitatively, we recently have studied phonon±plasmon mixing by using an 11-band tight binding model for the electronic bandstructure of the CuO plane, while the electronic bandstructure along the c-axis was introduced from the outside applying suitable interlayer couplings in parametrized form. In the present calculation the electronic bandstructure employed for the calculation of P and e, respectively, results from a complete tight-binding representation of the first-principles LAPW data including La 5d, Cu 3d, 4s, 4p and O 2p states (31-band model). No additional assumptions concerning the interlayer coupling are introduced in contrast to the 11-band model. Besides the nonadiabatic regime along the L $ 0Y 0Y 1 direction where dynamical screening and phonon±plasmon mixing comes into play, the phonon dispersion is also calculated for the main symmetry directions using the adiabatic approximation, i.e. assuming static screening. Besides other features, from this calculation the growing importance of the itinerant component of the charge response in the CuO plane to achieve high-T c values can be extracted. The charge fluctuations and the self-consistent changes of the crystal potential at the ion sites as induced by the symmetrical apical oxygen breathing mode at the Z point (O z Z ), being important for nonlocal electron±phonon interaction and pair binding, are calculated for the phonon-like and plasmon-like modes. Furthermore, a comparison is made with recent inelastic neutron scattering results for certain phonon anomalies. Finally, a possible solution concerning the apparent inconsistency of the current interpretation of the neutron c-axis data with the infrared c-axis optical spectra in La 2 CuO 4 is shortly outlined. Based on this discussion, the possibility for the application of a typical (LDA) bandstructure result for the description of the c-axis response in LaCuO the other HTSCs is estimated.

Phonons, electronic charge response and electron–phonon interaction in the high‐temperature superconductors

“…( 5) for the dynamical matrix selfconsistently. The z-polarized 1 Λ branches are the only phonons that couple strongly with the CF [32,46]. We shall demonstrate that whether one observes metallic screening effects of the 1 Λ modes depends on the frequency of the c-axis plasmon in comparison to the phonon frequencies.…”

“…4) is formed in model M5. As far as the EPI is concerned we find for the more moderate anisotropy in M4 and M5 large contributions for V κ δ from the plasmon-like and the phonon-like modes, while for an even less anisotropic regime the plasmon-like mode dominates [32,46]. Finally, in the adiabatic regime the coupling is strongly reduced.…”

“…Modes outside the non-adiabatic region, see Subsection 3.4, can be well described in the adiabatic approximation. Only for X B O a small non-adiabatic correction of about 0.1 THz has been found which can be attributed to Fermi surface nesting [46]. In Fig.…”

“…4. As discussed in [31] a typical LDA-like bandstructure within the 31BM [46] taken as input for the calculation of the electronic polarizability Π is not able to describe the strong anisotropy of the charge response in the c-direction seen in the experiments, while the charge response in the CuO plane is quite well represented.…”

Impact of dynamical screening on the phonon dynamics of metallicLa2CuO4

“…the DFT-LDAlike bandstructure is not anisotropic enough. It should be remarked that an earlier calculation within the 31BM 47 neglecting dipole fluctuations as additional electronic polarization processes besides the charge fluctuations still further enhances the deviations between the calculated and the measured result for the Λ 1 -modes. Anisotropic DF's being particular important along the c-axis and for ions in the ionic layers 43 have been taken into account in the calculations shown in Fig.…”