Fyzikální ústav Akademie věd ČR

Seminář Úterý, 21.06.2016 15:00 - 16:00

Přednášející: Richard Hlubina (Department of Experimental Physics, Comenius University, Bratislava, Slovakia)
Místo: Na Slovance, přednáškový sál v přízemí
Jazyk: anglicky
Pořadatelé: Oddělení teorie kondenzovaných látek

Abstract: In this talk I will describe how the single-particle properties of superconductors are influenced by the dominant scattering processes to which the electrons are subject. I will start by discussing the inelastic processes and I will show that in addition to the well known pairing modes, also pair-breaking modes may couple to the electrons. I will argue that since both kinds of modes lead to similar kinks of the electron dispersion curves, photoemission spectroscopy can not be straightforwardly applied in search for the pairing glue of superconductors. Fortunately, in BCS-like superconductors, the momentum-dependence of the normal and anomalous self-energy can be neglected, and in this case manipulation with the data does allow us to extract the gap function ∆(ω) and therefore also the pairing glue. However, in the cuprates such a procedure may not be justified. Instead, I will point out that the pairing glue is in this case more directly visible in the spectral function of the Nambu-Gor’kov anomalous propagator and I will demonstrate that this function is in principle experimentally observable [1].
In the second part of this talk I will concentrate on the effect of elastic scattering on the spectral properties of superconductors. It has long been well known that excellent fits of the tunneling density of states in dirty superconductors can be often achieved making use of the phenomenological Dynes formula. However, no consistent derivation of this formula has been available so far. I will argue that there exists a generic mechanism which can explain the Dynes formula: the key requirement is that a continuous distribution of pair-breaking fields should be present. I will show that, within the coherent potential approximation, a Lorentzian distribution of such pair-breaking fields does lead to the Dynes formula, regardless of the type and magnitude of the pair-conserving potential disorder. Going beyond the Dynes phenomenology, I will also present the simplest consistent generalization of the BCS Green’s function which takes into account both, the pair-conserving and the pair-breaking scattering processes [2].

[1] T. Bzdušek and R. Hlubina, Philosophical Magazine 95, 609-621 (2015)
[2] F. Herman and R. Hlubina, arXiv:1606.02983