Orbital-selective correlations and block magnetism in low-dimensional iron-based superconductors*

The discovery of superconductivity in Fe-based two-leg ladder materials under high pressure [1] has opened new directions to improve our understanding of pairing tendencies in iron-based superconductors. Computational calculations of strongly correlated electronic models can be performed with high accuracy in quasi one dimension, including the case of multi-orbital systems. Using numerical techniques, such as DMRG, multi-orbital Hubbard models were studied at various Hubbard and Hund couplings, and electronic densities. We have found clear indications of pairing in slightly doped chains [2] and ladders [3]. The magnetic properties observed in these systems are also rich, including the observation of an ``orbital selective Mott Phase'' in a wide parameter range. This phase is characterized by the formation of magnetic block states where a block of N spins "up" alternate with a block of N spins "down" [4,5,6,7]. We were able to calculate the dynamical spin structure factor and interpret the results in terms of a mixture of acoustic and optical modes [4,6,7] in agreement with neutron scattering experiments. This complex behavior observed in models for the Fe-based superconductors in low dimensions when studied with unbiased techniques indicates that the physics of these materials can hide several surprises.

References:

[1] H. Takahashi et al., Nat. Mater. 14, 1008 (2015); J. Ying et al., PRB 95, 241109(R) (2017).
[2] N. Patel et al., PRB 96, 024520 (2017)
[3] N. Patel et al., PRB 94, 075119 (2016)
[4] J. Herbrych et al., Nat. Comm. 9, 3736 (2018)
[5] J. Herbrych et al., PRL 123, 027203 (2019)
[6] J. Herbrych et al., PNAS 117, 16226 (2020)
[7] J. Herbrych et al., Phys. Rev. B 102, 115134 (2020).