O.V. Dolgov

Electronic states and optical spectra of HTSC with electron-phonon coupling

Abstract It is shown that due to the strong electron-phonon interaction the usual Fermi-liquid description of the electron system is violated in the normal phase of HTSC metals ( T > T c ). As a result it is impossible to use the simple formulas of the Drude type for the calculation of FIR properties of the HTSC materials. The many-body calculation of the reflectivity gives a good agreement with the FIR measurements for the single-domain crystal. The processing of the obtained results by using the “extended Drude formula” gives the effective scattering rate 1/τ ∗ ≈βħω where β is about 1 up to 2000 cm -1 (and even for higher frequencies taking into account the interband transitions).

THERMAL PAIR-BREAKING IN SUPERCONDUCTORS WITH STRONG ELECTRON-PHONON INTERACTION

Abstract The influence of inelastic scattering in superconductors with a strong electron- phonon interaction was considered. The pair-breaking scattering leads to smearing of singularities in the electron density of states and to the appearance of states inside a “gap”. Normal electrons in such superconductors appear due to the filling of the states instead of the excitations across the gap. This leads to the temperature dependencies of some thermodynamic and kinetic characterics to be more close to the phenomenological Gorter-Casimir two-fluid model rather then BCS theory.

Far-infrared properties of high Tc superconductors

Abstract The results of calculations of the optical conductivity σ ( ω , T ) and reflectivity R ( ω , T ) are presented. These calculations were carried out in the frame of the Eliashberg theory, the function of electron-phonon interaction being obtained from tunneling measurements. The obtained frequency and temperature dependencies have a rather good agreement with experimental data.

Impurities in multiband superconductors

Disorder - impurities and defects violating an ideal order - is always present in solids. It can result in interesting and sometimes unexpected effects in multiband superconductors. Especially if the superconductivity is unconventional thus having other than the usual s-wave symmetry. This paper uses the examples of iron-based pnictides and chalcogenides to examine how both nonmagnetic and magnetic impurities affect superconducting states with

Tracing the

s_pm

s_\pm

and

-symmetry in iron pnictides by controlled disorder

s_{++}

Optical response of Ba 1 − x K x BiO 3 : Evidence for an unusual coupling mechanism of superconductivity

order parameters. We show that disorder causes the transitions between

Microwave conductivity of superconductors with a strong electron-phonon interaction

s_pm

Strong-coupling effects in s-wave two-band superconductor

and