Who: Dmitri Efremov, Leibnitz Institute for Solid State Physics and Material Science IFW-Dresden
Place: Donostia International Physics Center
Date: Wednesday, 25 July 2018, 12:00
Determination of the symmetry of the superconducting order parameter is the most important and at the same time the most complicated step in elucidating the mechanism of superconductivity. One of the recent approach is the systematic study of the evolution of properties of a superconductor to introduced disorder. In this talk the effect of disorder in multiband superconductors (such as Fe-based pnictides) will be reviewed [1,2]. It will be shown that impact of impurities in multiband superconductors is beyond of a common wisdom: the impurities in s+- superconductors suppress Tc in the same way as paramagnetic ones in common superconductors, and vice versa magnetic impurities act as nonmagnetic ones. Impurities (nonmagnetic as well as magnetic) themselves can give rise new phenomena like change of the symmetry of superconductive order parameter. As a result, intrinsically phase-insensitive experimental methods like tunneling, ARPES, terahertz spectroscopy may be used for revealing of information about the underlying order parameter symmetry. Finally an investigation of a Ba(Fe0.9Co0.1)2As2 thin film by THz spectroscopy and stepwise proton irradiation will be presented . The evolution of the optical conductivity with irradiation dose is explained by the change from sign-reversed (są) to sign-preserved (s++) symmetry. It signals that są symmetry is realized in the pristine sample. Summarizing, in the
talk it will be shown that systematic study of the response to introduced disorder to a superconductor is a phase-sensitive tool to probe the order parameters of superconductors.
 D.V. Efremov, M.M. Korshunov, O.V. Dolgov, A.A. Golubov, P.J. Hirschfeld, Phys. Rev. B 84, 1805512R (2011.
 D. V. Efremov, S.-L. Drechsler, H. Rosner, V. Grinenko, and O. V. Dolgov, Phys. Status Solidi B. doi:10.1002/pssb.201600828 (2017)
 Micha Benjamin Schilling, Andreas Baumgartner, Boris Gor- shunov, Elena Zhukova, Valery Dravin, Kiril Mitsen, Dmitri Efremov, Oleg Dolgov, Kazumasa Iida, Martin Dressel, Sina Zapf, Phys. Rev. B 93, 174515 (2016)
Host: V. Silkin