No abstract

No abstract

The two-orbital J 1 -J 2 model that describes a square lattice of frustrated spin-1 iron atoms is analyzed within the linear spin-wave approximation and by exact diagonalization over a 4 ϫ 4 cluster. A quantum critical point ͑QCP͒ is identified that separates hidden magnetic order at weak Hund's rule coupling from a commensurate spin-density wave ͑cSDW͒ at strong Hund's rule coupling. Although the moment for cSDW order is small at the QCP, the critical linear spin-wave spectrum shows strong low-energy excitations centered at the wave numbers that correspond to cSDW order. These disperse anisotropically. A fit to the magnetic excitation spectrum of ferropnictide materials obtained recently by inelastic neutron-scattering measurements notably accounts for the absence of softening at the wave number that corresponds to Néel order.

The wavefunction renormalization Z(k′, ω) that appears on the right-hand side of the Eliashberg Equations listed in equation (58) of section 4.2 and in equations (D.1), (D.2) and (D.3) of appendix D must be replaced by Z(k′, ω′), where ω′ = E(k′). It must also be added that the subsequent Eliashberg equations (59a) and (59b) in section 4.3 are achieved under the approximation that the above corrected wavefunction renormalization on the righthand side of equation (58) is replaced by its value at the Fermi level: Z(k′, ω) as ω→0. These corrections and clarifications do not change any of the results and conclusions obtained in the paper. ORCID iDsJose P Rodriguez https:/ /orcid.org/0000-0002-5169-6883

A Heisenberg model over the square lattice recently introduced by Si and Abrahams to describe local-moment magnetism in the new class of Fe-As high-T(c) superconductors is analyzed in the classical limit and on a small cluster by exact diagonalization. In the case of spin-1 iron atoms, large enough Heisenberg exchange interactions between neighboring spin-1/2 moments on different iron 3d orbitals that frustrate true magnetic order lead to hidden magnetic order that violates Hund's rule. It accounts for the low ordered magnetic moment observed by elastic neutron diffraction in an undoped parent compound to Fe-As superconductors. We predict that low-energy spin-wave excitations exist at wave numbers corresponding to either hidden Néel or hidden ferromagnetic order.