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Speakers: Tadeusz Domański (Institute of Physics, M. Curie-Skłodowska University, 20-031 Lublin, Poland)
Place: Na Slovance, main lecture hall
Presented in English
Organisers:
Department of Condensed Matter Theory
Abstract: Superconductivity arises from the pairing of electrons in the vicinity of the Fermi energy. Transition to the superconducting state occurs at a critical temperature Tc when the gauge symmetry of the system spontaneously breaks down due to appearance of a complex order parameter Ψ = Χ eiφ. Physically, the amplitude Χ describes the density of the electron pairs and it indirectly shows up via the energy gap of electronic excitations. The other (phasal) degree of freedom φ controls coherence between the electron pairs -- in particular, any spatial inhomogeneity ∇φ ≠ 0 generates microscopic supercurrents. In this lecture I shall address the role of superconducting fluctuations observable upon approaching the true phase transition Tc from above and from below. Amplitude fluctuations give rise to inhomogeneity of the local energy gap wheras fluctuations of the phase φ lead to a pseudogap and allow for remnants of the Meissner effect (due to the overdamped Goldstone mode) or the Bogoliubov-type quasiparticles surviving above Tc. These results shall be confronted with the recent experimental data obtained for cuprate superconductors and other strongly correlated fermion systems.
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