Spin dynamics of the block orbital-selective Mott phase

TL;DR

This paper theoretically investigates the spin dynamics in the orbital-selective Mott phase of iron-based superconductors, predicting features consistent with neutron scattering experiments and revealing novel local spin excitations.

Contribution

It provides the first theoretical prediction of the dynamical spin structure factor in the block-OSMP using DMRG, explaining experimental observations and identifying new local spin excitations.

Findings

Identification of low-energy dispersive spin-wave-like modes

Discovery of high-energy dispersionless local spin excitations

Agreement with neutron scattering experimental spectra

Abstract

Iron-based superconductors display a variety of magnetic phases originating in the competition between electronic, orbital, and spin degrees of freedom. Previous theoretical investigations of the multi-orbital Hubbard model in one dimension revealed the existence of an orbital-selective Mott phase (OSMP) with block spin order. Recent inelastic neutron scattering (INS) experiments on the BaFe$_2$Se$_3$ ladder compound confirmed the relevance of the block-OSMP. Moreover, the powder INS spectrum reveled an unexpected structure, containing both low-energy acoustic and high-energy optical modes. Here we present the theoretical prediction for the dynamical spin structure factor within a block-OSMP regime using the density-matrix renormalization group method. In agreement with experiments we find two dominant features: low-energy dispersive and high-energy dispersionless modes. We argue that the former represents the spin-wave-like dynamics of the block ferromagnetic islands, while the latter is attributed to a novel type of local on-site spin excitations controlled by the Hund coupling.