[seminar] IF-utorak

[seminarIF]

Poštovani,

obavještavam Vas o održavanju seminara na Institutu za fiziku, Bijenička cesta 46, predavaonica u zgradi Mladena Paića u utorak 16. rujna 2008. u 15:00 sati.

Seminar pod naslovom Strong-coupling theory of high-temperature superconductivity održat će prof. Sasha  Alexandrov, Loughborough University, Loughborough, United Kingdom.
Sazetak predavanja mozete pronaci u nastavku poruke.

Srdacan pozdrav,

Voditelji seminara IF-a
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Strong-coupling theory of high-temperature superconductivity

 
Sasha  Alexandrov

 

Loughborough University, Loughborough, United Kingdom




 

High-temperature superconductivity (HTS) is a challenge to the conventional BCS  theory. I present  a multi-polaron approach to the problem based on our extension of the BCS theory to the strong-coupling regime [1]. Attractive electron correlations,  prerequisite to  HTS, are caused by an almost non-retarded electron-phonon (e-ph) interaction sufficient to overcome the direct Coulomb repulsion in this regime. We have identified  the long-range  Froehlich electron-phonon interaction  as the most essential for pairing in novel superconductors owing to a poor screening, as now confirmed by ARPES and some other experimental studies. Low energy physics is that of superlight small polarons and bipolarons (real-space electron (hole) pairs dressed by phonons). They are itinerant quasiparticles existing in the Bloch states at temperatures below the characteristic phonon frequency. Applying a continuous-time quantum Monte-Carlo algorithm (CTQMC) we present exact coherent band dispersions and the density of states of lattice (bi)polarons in the region of parameters where any approximation might fail. Many experimental observations have been predicted or understood in the framework of our "Froehlich-Coulomb" model, including pseudo-gaps, in-plane and c-axis normal state transport, anisotropy, isotope effects, upper critical fields, the normal state Nernst effect, diamagnetism, and the Hall-Lorenz numbers. Magnetic quantum oscillations recently observed in a few cuprate superconductors are also discussed.

 

[1] A.S. Alexandrov,  "Theory of Superconductivity: From Weak to Strong Coupling"

(IoP Publishing, Bristol and Philadelphia, 2003).
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