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TT: Fachverband Tiefe Temperaturen

TT 32: SC: Fe-based Superconductors - Theory

TT 32.3: Vortrag

Mittwoch, 16. März 2011, 11:00–11:15, HSZ 304

Self-consistent spin wave theory in the collinear phase and its application to iron pnictides — •Daniel Stanek¹, Michael Holt², Oleg P. Sushkov², and Götz S. Uhrig¹ — ¹Lehrstuhl für Theoretische Physik I, Technische Universität Dortmund, 44221 Dortmund, Germany — ²School of Physics, University of New South Wales, Kensington 2052, Sydney NSW, Australia

A possibility to describe magnetism in the iron pnictide parent compounds in terms of the two dimensional frustrated Heisenberg J₁-J₂ model has been actively discussed recently. However, neutron scattering studies have revealed the three dimensional character of the magnetism in the iron pnictides and an anisotropy between the exchange perpendicular and parallel to the spin stripes. Based on these observations, we study the J₁-J₂-J_c model as the three dimensional generalization of the J₁-J₂ model for S=1 and S=1/2. Using self-consistent spin wave theory, we present a detailed description of the staggered magnetization and magnetic excitations in the collinear state. Interestingly, two qualitatively distinct ways are found how the collinear, magnetically long-range ordered phase becomes unstable. Either the magnetization or one of the spin wave velocities vanishes. In addition, we discuss the relevance of a biquadratic exchange, which explains a part of the anisotropy between the effective in-plane exchange constants on the level of self-consistent spin wave theory.

In the application for the 122 iron pnictides, the experimentally measured spin wave dispersion is compared to the one derived within our model.