Berlin 2015 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 17: Superconductivity: Properties and Electronic Structure
TT 17.14: Vortrag
Montag, 16. März 2015, 18:30–18:45, H 2053
Elucidating superconductivity and intermediate valence of elemental Eu under high pressure — •Jürgen Röhler — Universität zu Köln, 50937 Köln, Germany
Elemental Eu is a superconductor under high pressure, P≥ 80 GPa, up to Tc = 2.75 K at 142 GPa [1]. We elucidate the possible connection between pressure induced 4f configurational changes, Eu2+(4f7, J=7/2) Eu3+ (4f6, J=0), and superconductivity. Notably high pressure LIII XAS [2] and more recently also ME isomer shift measurements [3] do not show the theoretically expected 2+ - 3+ transition, but intermediate valence states saturating at v≃ 2.6 between ∼ 20 and 70 GPa, and undergoing between 31 and 37 GPa a transformation into a complex incommensurately modulated monoclinic structure ∼ α-U, which is followed by an other hitherto unidentified low-symmetry complex structure. We discuss how the Brillouin zone - Fermi surface interaction, driven by the non integer valence electron count, may stabilize low-symmetry complex structures, which tend to favor the occurrence of superconductivity through bandstructures with overlapping electron and hole bands.
[1] M. Debessai et al., Phys. Rev. Lett. 102, 197002 (2009).
[2] J. Röhler, Physica 144B, 27 (1986).
[3] W. Bi et al., Phys. Rev. B 85, 205134 (2012).