Roland Zeyher

Superconductivity-induced phonon self-energy effects in high-T c superconductors

The superconductivity-induced self-energy of phonons has been calculated in the lowest-order conserving approximation using conventional strong-coupling theory and also including scattering at nonmagnetic impurities. Results for the dependence of the shift and the width of phonons on temperature and scattering rates are presented and their sensitivity on the strength of the electron-phonon coupling and on impurities is pointed out. The theory is applied to optical data in YBa2Cu3O7 using the experimental one-phonon density, the value ofTc and [*=0.25 as inputs. Neglecting anisotropies and the momentum dependence of the electron-phonon coupling the resulting strong-coupling model with λ≈2.9 yields results which are in good agreement with the data, in particular, if impurity scattering is taken into account.

Phonon self-energy effects due to superconductivity: Evidence for the strong-coupling limit in YBa2Cu3O7-δ

Abstract The self-energy of phonons due to superconductivity is calculated in the weak and the strong coupling limit. Applying the theory to YBa2Cu3O7−δ we find the following results: a) The signs of the observed q = 0 phonon shifts due to superconductivity disagree in general with the predictions of the weak-coupling case; this result suggests that electronic transitions are not responsible for the electron pairing; b) the magnitude of the observed shifts (as well as the value of Tc) can consistently and semi-qunatatively be explained by assuming the strong-coupling limit with λ ∼ 2.9.

INTERPLAY BETWEEN SUPERCONDUCTIVITY AND FLUX PHASE IN THE T-J MODEL

We study the phase diagram of the

Holstein model in infinite dimensions at half-filling

t\ensuremath{-}J

Theory of multiphonon raman spectra above the energy gap in semiconductors

model using a mean field type approximation within the Baym-Kadanoff perturbation expansion for Hubbard X operators. The line separating the normal state from a d-wave flux or bond-order state starts near optimal doping at

Momentum dependence of the electron-phonon coupling and self-energy effects in superconducting YBa2Cu3O7 within the local density approximation.

T=0

Influence of static dipole moments on the lattice dynamics of PbI2

and rises quickly with decreasing doping. The transition temperature

Superconductivity Via Exchange Interactions and Antiferromagnetic Fluctuations in High-Tc Oxides

{T}_{c}

Statics and dynamics of charge fluctuations in the t-J model.

for d-wave superconductivity increases monotonically in the overdoped region towards optimal doping. Near optimal doping a strong competition between the two d-wave order parameters sets in leading to a strong suppression of

Superconductivity from orbital nematic fluctuations

{T}_{c}