The parent compounds of iron pnictide superconductors are bad metals with a collinear
antiferromagnetic structure and Néel temperatures below 220 K. Although alkaline iron
selenide A y Fe1. 6+ x Se2 (A= K, Rb, Cs) superconductors are isostructural with iron
pnictides, in the vicinity of the undoped limit they are insulators, forming a block
antiferromagnetic order and having Néel temperatures of roughly 500 K. Here we show that
the spin waves of the insulating antiferromagnet Rb0. 89Fe1. 58Se2 can be accurately …

Superconductivity in alkaline iron selenide AFe 1.6+ x Se 2 (A= K, Rb, Cs) may have a
different origin from the sign reversed s-wave electron pairing mechanism, because they are
insulators near x= 0 and form a blocked AF structure that is completely different from the iron
pnictides. We use neutron scattering to map out spin waves in the AF insulating Rb 0.89 Fe
1.58 Se 2. A comparison of the fitted effective exchange couplings using a local moment
Heisenberg Hamiltonian in Rb 0.89 Fe 1.58 Se 2,(Ba, Ca, Sr) Fe 2 As 2, and iron …