Spin dynamics within the block orbital-selective Mott phase in one dimensional iron chains and ladders

Iron-based superconductors display a variety of magnetic phases originating in the competition between electronic, orbital, and spin degrees of freedom. Theoretical investigations [1] of the 1D multiorbital Hubbard model revealed the existence of an orbital-selective Mott phase (OSMP) with block spin order, i.e., antiferromagnetically coupled ferromagnetic (FM) spin islands. Recent inelastic neutron scattering experiments on quasi-1D BaFe₂Se₃ and doped RbFe₂Se₃ compounds confirm the relevance of the spin-block phases [2-4]. Moreover, the spectrum unveiled exotic features in the dynamical spin structure factor S(q,ω) including a low-energy acoustic mode and a high-energy optical mode. In our work [5] we present the first theoretical study of the S(q,ω) within the block-OSMP using the DMRG method. In agreement with experimental results we find: a dispersive (acoustic) mode for momentum q<π/2, which arises from the dynamics of FM islands, and a dispersion-less (optical) mode for q>π/2 attributed to local block Hund excitations.

[1] J. Rincon et al., Phys. Rev. Lett. 112, 106405 (2014)
[2] M. Wang, et al., Nature Comm. 2, 580 (2011)
[3] M. Wang, et al., Phys. Rev. B 94, 041111(R) (2016)
[4] M. Mourigal, et al., Phys. Rev. Lett. 115, 047401 (2015)
[5] J. Herbrych, et al., In preparation