Block-spiral magnetism: An exotic type of frustrated order

Abstract

Competing interactions in Quantum Materials induce novel states of matter such as frustrated magnets, an extensive field of research both from the theoretical and experimental perspectives.Here, we show that competing energy scales present in the low-dimensional orbital-selective Mott phase (OSMP) induce an exotic magnetic order, never reported before. Earlier neutron scattering experiments on iron-based 123 ladder materials, where OSMP is relevant, already confirmed our previous theoretical prediction of block-magnetism (magnetic order of the form ↑↑↓↓). Now we argue that another novel phase can be stabilized in multiorbital Hubbard models, the "block-spiral state". In this state, the magnetic islands form a spiral propagating through the chain but with the blocks maintaining their identity, namely rigidly rotating. This new spiral state is stabilized without any apparent frustration, the common avenue to generate spiral arrangements in multiferroics. By examining the behaviour of the electronic degrees of freedom, parity breaking quasiparticles are revealed. Finally, a simple phenomenological model that accurately captures the macroscopic spin spiral arrangement is also introduced.

Block orbital-selective Mott insulators: a spin excitation analysis

“…In the "standard" metallic state (as in the small U single-orbital Hubbard model), the magnetic moments S 2 = S(S + 1) are small. This is in contrast to the spin's behavior within OSMP in the metallic regime, with itin-erant electrons coexisting [44,46,48] with well-developed local magnetic moments. Such coexistence creates a rich magnetic phase diagram within OSMP.…”

“…Arrows indicate the representative spin order. and (iii) energy gap in the single-particle spectral function (different to the behaviour of the metallic bands with finite spectral weight at the Fermi level) [48,54].…”

“…2. The FM phase and block-magnetic phase are separated by an exotic blockspiral phase [48] where blocks maintain their character and start to rotate rigidly. We refer the interested reader to Ref.…”

“…We refer the interested reader to Ref. 48 for details about this novel frustrated state which will not be addressed further in this publication.…”

“…Also, it is worth noting that: (a) the J 1 -J 2 model was used in Ref. [47] to describe the spin spectrum of the three-orbital chain and two-orbital ladder systems, and (b) a similar model with leading consecutive FM and AFM interactions was used in the analysis [48] of the block-spiral state [i.e. the state stable in the vicinity of block-magnetism, see Fig.…”