Charge Dynamics of Doped Holes in HighTcCuprate Superconductors: A Clue from Optical Conductivity (original) (raw)
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Physical Review B, 2014
Electronic interactions in multiorbital systems lead to non-trivial features in the optical spectrum. In iron superconductors the Drude weight is strongly suppressed with hole-doping. We discuss why the common association of the renormalization of the Drude weight with that of the kinetic energy, used in single band systems, does not hold in multi-orbital systems. This applies even in a Fermi liquid description when each orbital is renormalized differently, as it happens in iron superconductors. We estimate the contribution of interband transitions at low energies. We show that this contribution is strongly enhanced by interactions and dominates the coherent part of the spectral weight in hole-doped samples at frequencies currently used to determine the Drude weight.
Hot Spots and Pseudogaps for Hole- and Electron-Doped High-Temperature Superconductors
Physical Review Letters, 2004
Using cluster perturbation theory, it is shown that the spectral weight and pseudogap observed at the Fermi energy in recent Angle Resolved Photoemission Spectroscopy (ARPES) of both electron and hole-doped high-temperature superconductors find their natural explanation within the t-t ′-t ′′-U Hubbard model in two dimensions. The value of the interaction U needed to explain the experiments for electron-doped systems at optimal doping is in the weak to intermediate coupling regime where the t − J model is inappropriate. At strong coupling, short-range correlations suffice to create a pseudogap but at weak coupling long correlation lengths associated with the antiferromagnetic wave vector are necessary.
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Physical Review B, 1991
The infrared absorption of the 155-cm c-axis mode of YBa2Cu307 is calculated on the basis of an anharmonic-electron-phonon-interaction model and a large enhancement of its intensity is obtained. A double-well potential in the electron-phonon interaction gives the right order of magnitude for shifts in the bridging O(4) position in agreement with recent extended x-ray-absorption fine-structure data. Electron-density-two-phonon-interaction terms are derived which represent a violation of the Migdal theorem and a BCS-type superconducting state with nonlinearly enhanced electron-phonon coupling is expected together with an anisotropy of the superconducting energy gap.
Where do holes go in doped antiferromagnets and what is their relationship to superconductivity?
Journal of Physics and Chemistry of Solids, 2002
We discuss the tendency of doped holes to form quasi-one-dimensional structures (`stripes'), as observed in high-T c materials. We compare single-particle spectral functions of strongly-correlated models with recent angle-resolved-photoemission results for LaSrCuO and LaNdSrCuO materials, allowing us to distinguish between different stripe con®gurations. In particular, for low dopings, our results indicate a bond-centered structure, whereas at higher dopings, holes prefer to proliferate into the antiferromagnetic domains. Furthermore, we discuss the competition between stripes and superconductivity. In particular, we show an enhancement of long-distance superconducting correlations produced by the long-range part of the Coulomb interaction. q
Modern Physics Letters B
Within the framework of kinetic-energy-driven superconductivity, the asymmetric doping dependence of superconductivity between the hole- and electron-doped triangular-lattice superconductors has been studied. It is shown that although the superconducting transition temperature has a dome-shaped doping dependence for both the hole- and electron-doped triangular-lattice superconductors, superconductivity appears over a wide range of doping in the hole-doped case, while it only exists in a narrow range of doping in the electron-doped case. Moreover, the maximum superconducting transition temperature around optimal doping in the electron-doped triangular-lattice superconductors is lower than that of the hole-doped counterparts. The theory also shows that the asymmetric doping dependence of superconductivity between the hole- and electron-doped cases may be a common feature for a doped Mott insulator.
Unconventional superconductivity mediated solely by isotropic electron-phonon interaction
Physical Review B
Unconventional superconductivity is commonly linked to electronic pairing mechanisms, since it is believed that the conventional electron-phonon interaction (EPI) cannot cause sign-changing superconducting gap symmetries. Here, we show that this common understanding needs to be revised when one considers a more elaborate theory of electron-phonon superconductivity beyond standard approximations. We self-consistently solve the full-bandwidth, anisotropic Eliashberg equations including vertex corrections beyond Migdal's approximation assuming the usual isotropic EPI for cuprate, Fe-based, and heavy-fermion superconductors with nested Fermi surfaces. In the case of the high-T c cuprates we find a d-wave order parameter, as well as a nematic state upon increased doping. For Fe-based superconductors, we obtain s ± gap symmetry, while for heavy-fermion CeCoIn 5 we find unconventional d-wave pairing. These results provide a proof of concept that EPI cannot be excluded as a mediator of unconventional and of high-T c superconductivity.
Physical Review B, 2003
We show that, at weak to intermediate coupling, antiferromagnetic fluctuations enhance d-wave pairing correlations until, as one moves closer to half-filling, the antiferromagnetically-induced pseudogap begins to suppress the tendency to superconductivity. The accuracy of our approach is gauged by detailed comparisons with Quantum Monte Carlo simulations. The negative pressure dependence of Tc and the existence of photoemission hot spots in electron-doped cuprate superconductors find their natural explanation within this approach.
Optical conductivity and Raman scattering of iron superconductors
Physical Review B, 2013
We discuss how to analyze the optical conductivity and Raman spectra of multi-orbital systems using the velocity and the Raman vertices in a similar way Raman vertices were used to disentangle nodal and antinodal regions in cuprates. We apply this method to iron superconductors in the magnetic and non-magnetic states, studied at the mean field level. We find that the anisotropy in the optical conductivity at low frequencies reflects the difference between the magnetic gaps at the X and Y electron pockets. Both gaps are sampled by Raman spectroscopy. We also show that the Drude weight anisotropy in the magnetic state is sensitive to small changes in the lattice structure.