Band Narrowing and Mott Localization in Iron OxychalcogenidesLa2O2Fe2O(Se,S)

Abstract

Bad metal properties have motivated a description of the parent iron pnictides as correlated metals on the verge of Mott localization. What has been unclear is whether interactions can push these and related compounds to the Mott-insulating side of the phase diagram. Here we consider the iron oxychalcogenides La2O2Fe2O(Se,S)2, which contain an Fe square lattice with an expanded unit cell. We show theoretically that they contain enhanced correlation effects through band narrowing compared to LaOFeAs, and we provide experimental evidence that they are Mott insulators with moderate charge gaps. We also discuss the magnetic properties in terms of a Heisenberg model with frustrating J1-J2-J2' exchange interactions on a "doubled" checkerboard lattice.

Weak spin interactions in Mott insulating La2O2Fe2OSe2McCabe1, Stock2, Rodriguez3 et al. 2014Phys. Rev. B4527630View full textAdd to dashboardCite

“…Analogous to the cuprates, the spin exchange constants and spin-wave dispersions in these parent compounds are large, extending up to energy transfers of ∼100 meV, reflecting strong Fe-Fe coupling [19][20][21][22][23][24]. Electronic structure calculations for La 2 O 2 Fe 2 OSe 2 suggest similar exchange constants to the pnictides but with considerable electronic band narrowing [14]. Until now, neutron inelastic measurements to corroborate such predictions have not been reported for La 2 O 2 Fe 2 OSe 2 .…”

Site-selective electronic structure of pure and doped Ca2O3Fe3S2

“…In this context, finding insulating and antiferromagnetically ordered ground states in layered Fe-oxychalcogenides [11,12,14,18,19] is relevant, since it confirms theoretical suggestions that Mott-insulating parent compounds in the Fesuperconducting systems could be found by increasing the ratio of the interaction to hopping beyond a critical value for a Mott transition [20]. The Fe-oxychalcogenides [2] thus help to sharpen the fundamental debate [21] on the degree of electronic correlations in Fe-based superconductors in general.…”

“…Given telling similarities, along with notable differences, between the ironand cuprate-based superconductors [8], an especially important issue has been to confirm whether the parent compounds are itinerant metals or if they lie in close proximity to a Mott metal-to-insulator transition [7,9]. Particularly interesting for the latter view are Fe-oxychalcogenides, which have been synthesized with various compositions [2,[10][11][12][13][14], showing different degrees of electron localization.…”

“…Our parameter choice for the on-site Coulomb interaction is consistent with the U value used in Ref. [13] and the underlying view that Fe-oxychalcogenides are better regarded as strongly correlated electron systems [14]. We evaluated the many-particle Green's functions of the Hamiltonian H = H 0 + H int above at Sites 1 and 2 within LDA+DMFT [24], using MO iterated perturbation theory (MO-IPT) as impurity solver [36].…”

“…The Fe-oxychalcogenides [2] thus help to sharpen the fundamental debate [21] on the degree of electronic correlations in Fe-based superconductors in general. However, finding Mott electrons with different degrees of activation energies [11][12][13][14]18] suggests strong multiorbital (MO) electronic localization in this material class. In contrast to Fe-based superconductors, the consequences of Mottness (or the proximity to a insulator-metal transition) upon external perturbations in the Fe-oxychalcogenides has not received the theoretical attention it deserves.…”