Spin dynamics of the block orbital-selective Mott phase

J Herbrych,G Alvarez,A Moreo,N Kaushal,E Dagotto,A Nocera

doi:10.1038/s41467-018-06181-6

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 BaFe2Se3 ladder compound confirmed the relevance of the block-OSMP. Moreover, the powder INS spectrum revealed 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.

Highlights

Iron-based superconductors display a variety of magnetic phases originating in the competition between electronic, orbital, and spin degrees of freedom
The model chosen was previously studied with regards to its timeindependent properties, and it is known that it displays an orbital-selective Mott phase (OSMP) regime in the ground state[23]
↓} at n‘;γ;σ orbital 1⁄4 cy‘;γ;σ γ= c‘;σ;γ is the local ð‘; γÞ electron density with spin σ. Note that another common labeling of these orbitals could be based on the canonical t2g manifold, i.e., {yz, xz, xy}, respectively. tγγ′ denotes a symmetric hopping amplitude matrix defined in the orbital space γ: t00 = t11 = −0.5, t22 = −0.15, t02 = t12 = 0.1, and t01 = 0, all in eV units (Fig. 1a displays a schematic representation of the Hamiltonian)

Summary

Introduction

Iron-based superconductors display a variety of magnetic phases originating in the competition between electronic, orbital, and spin degrees of freedom. One reason is that theoretical many-body calculations based on model Hamiltonians can be accurately performed in onedimension, numerically For this reason, it was exciting when a one-dimensional family of compounds containing two-leg ladders was unveiled in the iron-superconductors context. In the special case of BaFe2Se3 remarkably an exotic block magnetism was found[19,22,25,30,31] involving antiferromagnetically coupled ferromagnetic islands made of 2 × 2 iron clusters This unusual magnetic state was observed in the vicinity of suppeffiffircopndffiffiuctivity[32,33,34] in two-dimensional (2D) materials with 5 ́ 5 ordered iron vacancies, such as Rb0.89Fe1.58Se235 and K0.8Fe1.6Se236–38. The origin and characteristics of the optical modes, that are induced by shortdistance properties, have not been clarified so far

Methods

Results

Conclusion