Doping evolution of itinerant magnetic fluctuations in Fe-based pnictidesM. M. Korshunov1, 2 and I. Eremin1, 3
1 Max-Planck-Institut für Physik Komplexer Systeme - 01187 Dresden, Germany, EU
2 L.V. Kirensky Institute of Physics, Siberian Branch of Russian Academy of Sciences - 660036 Krasnoyarsk, Russia
3 Institute für Mathematische und Theoretische Physik, TU-Braunschweig - 38106 Braunschweig, Germany, EU
received 20 May 2008; accepted in final form 24 July 2008; published September 2008
published online 8 September 2008
Employing the four-band tight-binding model, we study theoretically the doping dependence of the spin response in the normal state of novel Fe-based pnictide superconductors. We show that the commensurate spin density wave (SDW) transition that arises due to interband scattering between the hole -pockets and the electron -pockets disappears already at the doping concentration x 0.04 reflecting the evolution of the Fermi surfaces. Correspondingly, with further increase of the doping the antiferromagnetic fluctuations are suppressed for x > 0.1 and the imaginary part of the spin susceptibility at antiferromagnetic wave vector becomes nearly temperature independent. At the same time, we observe that the uniform susceptibility deviates from the Pauli-like behavior and is increasing with increasing temperature reflecting the activation processes for the -Fermi surfaces up to temperatures of about T = 800 K. With increase of the doping the absolute value of the uniform susceptibility lowers and its temperature dependence changes. In particular, it is a constant at low temperatures and then decreases with increasing temperature. We discuss our results in a context of recent experimental data.
74.20.-z - Theories and models of superconducting state.
74.25.Ha - Magnetic properties.
75.30.Fv - Spin-density waves.
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