Low Energy Spin Excitations in Iron-Based Superconductors in a Minimum Single Band Model

We propose a tight-binding single band model for the newly discovered iron-selenide superconductors MxFe2-xSe2 (M = TI, K, Rb, Cs). The dispersion of the single band model consists of nearest-neighbor and next nearest-neighbor hoping integrals t1, t2. Similarly we consider the spin spin interactions among the spins of the electrons of the nearest-neighbor and next nearest-neighbor interactions with coupling J1 and J2. The spin interactions are considered within a mean-field approximation leading to spin density wave (SDW) antiferromagnetic order with a spin ordering wave vector, Q(pi, pi/2). The electron Green's functions are calculated from the Hamiltonian by using Zubarev's Green's function technique. Finally the spin density wave gap is calculated and solved self-consistently taking into account a magnetic phase-transition temperatures and their coupling constants.