Dresden 2009 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

TT: Fachverband Tiefe Temperaturen

TT 5: Postersession Superconductivity: Materials - Fabrication and Properties

TT 5.40: Poster

Montag, 23. März 2009, 13:00–16:45, P1A

Feedback spin resonance in the Fe-pnictide superconductors — •Alireza Akbari¹, Peter Thalmeier², Ilya Eremin¹, and Peter Fulde¹ — ¹Max Planck Institute for the Physcis of Complex Systems, D-01187 Dresden, Germany — ²Max Planck Institute for the Chemical Physics of Solids, D-01187 Dresden, Germany

The superconducting feedback resonance in inelastic neutron scattering has been found in numerous unconventional superconductors of the cuprate, heavy fermion type and recently in the FeAs class. This collective spin excitation in the 3d FeAs superconducting layers appears below T_c at an energy ω_r< 2Δ₀ and momentum transfer Q [Δ(k+Q)=−Δ(k)]. This resonance has been found in some Fe₂As₂ type superconductors and may be a more general phenomenon. An indirect evidence for enhanced Fe 3d spin dynamics in the superconducting state was recently observed in CeFeAsO_1−xF_x. The crystalline electric field (CEF) excitations of localized Ce 4f- states at 20 meV were found to couple weakly to the spin excitations in the FeAs layers leading to characteristic frequency shift and broadening effects. The temperature dependence of CEF excitations is studied within a RPA approximation. The experimental decrease of CEF excitation energy with temperature in the normal state is explained. Below T_c the feedback effect leads to an enhanced 3d spin response around 20 meV at Q=(π,π). The spectral shape and its temperature dependence of 3d and total 4f-3d spin dynamics are calculated. We compare the results to similar examples in the unconventional heavy fermion superconductors.