Fyzikální ústav Akademie věd ČR

Seminar Tuesday, 16/04/2013 15:00 - 16:00

Speakers: Alexander Shick (Department of Condensed Matter Theory, Institute of physics, ASCR, Prague; department of condensed matter physics, MFF UK Prague)
Place: Na Slovance, main lecture hall
Presented in English
Organisers: Department of Condensed Matter Theory

Abstract: A huge volume of research has resulted from the recent discovery of superconductivity in the RFeAsO series of compounds (where R represents a rare-earth element) characterized by its atomic-like 4f electrons. The replacement of this species by a member of the actinide series presents an exciting opportunity to study the effect of varying electron correlation. The successful substitution with actinides to form the AnFeAsO parent compounds (An=Np,Pu) has already been reported [1,2]. Both NpFeAsO and PuFeAsO materials order anti-ferromagnetically. In sharp contrast to the rare-earth analogs, no tetragonal-to-orthorhombic distortion is found. Instead, the negative thermal expansion is found in NpFeAsO below TN . I will present the results of the first-principles electronic structure calculations for the actinide-based oxypnictides, NpFeAsO and PuFeAsO, and make the comparison with the bulk experimental data.

PuCoGa5 has the highest critical temperature of 18.5 K among heavy-fermion superconductors, that is one order of magnitude higher than for typical heavy-fermion compounds. Spin and charge valence fluctuations may have an important role in mediation of the superconducting phase in the Pu-115 family of 5f-electron heavy-fermion superconductors. Specific character of the coupling mechanism remains uncovered. Very recent point-contact spectroscopy experiments [3] show that the paired superconducting electrons have wavefunction with the d-wave symmetry. I will address electron correlation effects in PuCoGa5and PuCoIn5 materials making use of a combination of the local density approximation with an exact diagonalization of the Anderson impurity model, and discuss the implications of the electronic structure to unexpected absence of magnetism, and the unconventional character of superconductivity in the Pu-115 compounds [4].

References
[1] T. Klimczuk et al., Phys. Rev. B 85, 174506 (2012).
[2] T. Klimczuk et al., Phys. Rev. B 86, 174510 (2012).
[3] D. Daghero et al., Nature Comm. 3, 1785 (2012).
[4] A. B. Shick, J. Kolorenc, J. Rusz, P. M. Oppeneer, A. I. Lichtenstein, M. I. Katsnelson, and R. Caciuffo, Phys. Rev. B 87, 020505 (2013).