Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 40: Superconductivity: Ferropnictides 1

TT 40.13: Vortrag

Donnerstag, 26. März 2009, 17:30–17:45, HSZ 03

Theory for magnetic excitations in Fe-pnictide superconductors — •Maxim Korshunov^1,2 and Ilya Eremin^1,3 — ¹Max-Planck-Institut für Physik komplexer Systeme, D-01187 Dresden, Germany — ²L.V. Kirensky Institute of Physics, Siberian Branch of RA, 660036 Krasnoyarsk, Russia — ³Institute für Mathematische und Theoretische Physik, TU Braunschweig, D-38106 Braunschweig, Germany

We analyze the spin response in the normal and superconducting states of the Fe-pnictide High-T_c superconductors. While the normal state spin excitations are dominated by the continuum of the interorbital antiferromagnetic (AFM) spin density wave fluctuations (SDW) and the incommensurate intraband SDW fluctuations, the unconventional superconductivity yields different feedback: the resonance peak in form of the well-defined spin exciton occurs only for the interband scattering at the AFM momentum Q_AFM for the extended s-wave (s_±) superconducting order parameter and it is extremely weak for the d-wave order parameter due to the specific Fermi surface (FS) topology. We discuss this essential difference in the context of neutron scattering experiments used for determination of the superconducting wave function symmetry.

For the non-superconducting state, we show that the commensurate AFM SDW transition disappears already at the doping concentration x ∼ 0.04 reflecting the evolution of the FS. Correspondingly, with further increase of the doping the AFM fluctuations are suppressed for x>0.1 and the Imχ(Q_AFM,ω)/ω becomes nearly temperature independent, in agreement with recent NMR experiments.