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

Abstract

Inelastic neutron scattering recently confirmed the theoretical prediction of a ↑↑↓↓-magnetic state along the legs of quasi-one-dimensional (quasi-1D) iron-based ladders in the orbital-selective Mott phase (OSMP). We show here that electron-doping of the OSMP induces a whole class of novel block-states with a variety of periodicities beyond the previously reported π/2 pattern. We discuss the magnetic phase diagram of the OSMP regime that could be tested by neutrons once appropriate quasi-1D quantum materials with the appropriate dopings are identified.Introduction. Competing interactions in strongly correlated electronic systems can induce novel and exotic effects. For example, in the iron-based superconductors [1][2][3][4] charge, spin, and orbital degrees of freedom combine phenomena known from cuprates with those found in manganites. Prominent among these novel effects is the orbital-selective Mott phase (OSMP) [5], where interactions acting on a multi-orbital Fermi surface cause the selective localization of electrons on one of the orbitals. As a consequence, the system is in a mixed state with coexisting metallic and Mott-insulating bands [ Fig. 1(a)]. Since the theoretical studies of the OSMP require the treatment of challenging multi-orbital models most of the investigations thus far were performed with approximations such as the the slave-particle mean field method [6][7][8][9] or dynamical mean-field theory [10][11][12]. Here, we present unambiguous numerical evidence of the OSMP within low-dimensional multi-orbital Hubbard models, unveiling a variety of new phases.The magnetic ordering associated with the OSMP could be significantly different from that observed in cuprates. The latter are described by single-band Hamiltonians and the parent compounds order in a staggered antiferromagnetic fashion. However, recent inelastic neutron scattering (INS) experiments [13] on quasi-1D ironbased materials of the 123 family (AFe 2 X 3 ; A alkali metals, X=Se,S chalcogenides) unveiled exotic π/2-block magnetic states where spins form antiferromagnetically (AFM) coupled ferromagnetic (FM) islands, in a ↑↑↓↓pattern [ Fig. 1(b)]. 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. We show that the block-OSMP magnetism can develop in various shapes and sizes depending on the electrondoping, far beyond the previously reported π/2-pattern. Moreover, here we develop effective Hamiltonians for the OSMP which allows for an intuitive understanding of the origin of block magnetism. Our simplified, yet accurate, model...

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.…”

Block–spiral magnetism: An exotic type of frustrated order

“…Note that these block patterns are not spin-density waves: The local expectation values of spin operators yield uniform magnetization throughout the system, unlike a spin wave that would have peaks and valleys. Our study, on the other hand, indicates a clear block structure with spins of the same magnitude at each site (26)(27)(28). Moreover, exact diagonalization results on small lattices (27) indicate that the block-OSMP ground state has a large overlap (at least 50%) with a state of the form | ↑↑↓↓ − | ↓↓↑↑ (as exemplified for the π/2 block).…”

“…Such a choice represents a generic case of coexisting wide and narrow electronic bands, as often found in iron-based materials from the 123 family (23,26,(37)(38)(39). The particular choice of the hopping matrix elements t γγ used here-specifically t00 = −0.5 [eV], t11 = −0.15 [eV], and t01 = t10 = 0-and crystal-field splitting ∆ = 0.8 [eV] is motivated by several previous studies (26)(27)(28) on the magnetic properties of the OSMP. The above values yield a kinetic energy bandwidth W = 2.1 eV which is used as an energy unit throughout this paper.…”

“…2) On the other hand, for BaFe2S3 and RbFe2Se3 INS reported (31-33) 2×1 blocks, FM along rungs and AFM along legs. Both of these phases are captured by the multiorbital Hubbard Hamiltonian (26) and also by its low-energy effective description (28), the generalized Kondo-Heisenberg model.…”

Pressure-induced collapse of large-moment magnetic order and localized-to-itinerant electronic transition in the host-guest compound [Cs6Cl][FAdler1, Medvedev2, Valldor3 et al. 2020Phys. Rev. B2010View full textAdd to dashboardCite

“…In the intermediate coupling regime, Hund's rule coupling J H plays an important role for the electronic properties of multiorbital systems and may lead to the formation of an orbitally selective Mott phase revealing coexistence of localized gapped and itinerant zero-gap electron bands [6]. In fact, the spin ladder compound BaFe 2 Se 3 was considered to be an example for an OSMP phase [32][33][34]. Given the similarities in the high-pressure phase diagrams of BaFe ] may also correspond to an orbitally selective Mott insulator state.…”