Spin dynamics of the block orbital-selective Mott phase

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.

Iron telluride ladder compounds: Predicting the structural and magnetic properties of BaFe2Te3

“…This conclusion agrees with our recent theoretical studies in n = 5.5 iron Te-based ladders [21]. Because many believe that the Block-type magnetic order of BaFe 2 Se 3 is related to an orbital selective Mott state induced by electronic correlations [28,[31][32][33], it is reasonable to conclude that BaFe 2 Te 3 could also display this interesting state as well. Of course, more powerful manybody techniques based on multiorbital Hubbard models are required to confirm this OSMP hypothesis.…”

“…For example, the existence of an "orbital-selective Mott phase" (OSMP) was found by neutron experiments at ambient pressure [30]. This OSMP of BaFe 2 Se 3 was theoretically discussed based on DMRG methods by using multiorbital Hubbard models as well [31][32][33]. However, an additional striking experimental discovery was recently reported for this interesting material: the existence of a polar state with possible polar orbital ordering was confirmed by neutron diffraction methods combined with optical second harmonic generation signals [34].…”

Novel Magnetic Block States in Low-Dimensional Iron-Based Superconductors

“…Similar patterns were also reported in two dimensions with iron vacancies, such as in Rb 0.89 Fe 1.58 Se 2 [14] and K 0.8 Fe 1.6 Se 2 [8,[15][16][17]. For the aforementioned compounds the OSMP state is believed to be relevant [8,13,[18][19][20].Recent theoretical investigations [21,22] showed that a multi-orbital Hubbard model in the OSMP state properly describes the INS spin spectra of π/2-block state of powder BaFe 2 Se 3 [13]. However, the origin of block magnetism and its relation to the OSMP is an intriguing and generic question that has been barely explored.…”

“…It is currently unknown if the latter approximates a pseudogap or rather a weak insulator, and more detailed analysis is needed.Block magnetism. Previous efforts [21,22] showed that the OSMP can display exotic magnetic properties, such as AFM coupled FM islands (the spin-block phase).Here, one of our main results is that the magnetic pattern of the block-OSMP is not limited to the π/2-phase, but remarkably the OSMP can support a variety of spin patterns previously unknown. Figure 2(a) illustrates the filling n dependence of the total spin structure factor S(q) [35].…”

Crossband versus intraband pairing in superconductors: Signatures and consequences of the interplay

“…To date, multiband electronic structure is proven to be of crucial importance in rather versatile superconducting systems, such as MgB 2 [10], iron-based compounds [11][12][13][14][15][16], superconducting nanostructures [17][18][19][20][21], 2D electron gases at interfaces [22][23][24], metal-organic superconductors [25][26][27], etc. In such multiband superconductors, the pairing interaction and the proximity/hybridization of two or more bands can result in the formation of Cooper pairs with electrons originating from different bands, a phenomenon termed "cross-band pairing" or simply "crosspairing".…”