Roman Micnas

Enhancements of the superconducting transition temperature within the two-band model

The two-band model as introduced by Suhl, Matthias and Walker [Phys. Rev. Lett. 3, 552 (1959)] accounts for multiple energy bands in the vicinity of the Fermi energy which could contribute to electron pairing in superconducting systems. Here, extensions of this model are investigated wherein the effects of coupled superconducting order parameters with different symmetries and the presence of strong electron-lattice coupling on the superconducting transition temperature Tc are studied . Substantial enhancements of Tc are obtained from both effects.

Theory of dynamic stripe induced superconductivity

Since the recently reported giant isotope effect on T* (Lanzara A et al 1999 J. Phys.: Condens. Matter 11 L541 and Rubio Temprano D et al 2000 Phys. Rev. Lett. 84 1990) could be consistently explained within an anharmonic spin-charge-phonon interaction model, we consider here the role played by stripe formation on the superconducting properties within the same model. This is a two-component scenario and we recast its basic elements into a BCS effective Hamiltonian. We find that the stripe formation is vital to high-Tc superconductivity since it provides the glue between the two components to enhance Tc to the unexpectedly large values observed experimentally.

The phase diagram of high-Tc superconductors in the presence of dynamic stripes

The phase diagram of superconducting copper oxides is calculated as a function of doping on the basis of a theory of dynamic stripe-induced superconductivity. The two major conclusions from the theory and the numerical analysis are that T* (the pseudogap onset temperature) and Tc (the superconductivity onset temperature) are correlated through the pseudogap, which induces a gap in the single-particle energies that persists into the superconducting state. On decreasing the doping the pseudogap ?* increases and T* increases, but when ?* exceeds a certain critical value the superconducting transition temperature Tc is lowered. A mixed s- and d-wave pairing symmetry is also examined as a function of doping.

Superconductivity in a Two-Component Model with Local Electron Pairs

AbstractSuperconductivity in the two-component model of coexisting local electron pairs (hard-core charged bosons) and itinerant fermions coupled via charge exchange mechanism is discussed. The cases of isotropic s-wave and anisotropic pairing of extended s-wave and

Polaronic origin of the isotope effect on the London penetration depth in high-temperature superconducting oxides

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Unconventional isotope effects as evidence for polaron formation in cuprates

symmetries are analyzed for a 2D square lattice within the BCS-mean-field approximation (MFA) and the Kosterlitz–Thouless theory. The phase diagrams and superconducting characteristics of this induced pairing model as a function of the position of the local pair (LP) level and the total carrier concentration are reviewed. The model exhibits crossovers between the BCS-like behavior and that of LPs. In addition, the Uemura plots are obtained for extended s and

Electron – lattice coupling in HTSC cuprates: Evidence for polaron formation from unconventional isotope and strain effects

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