Pairing Tendencies, Orbital Selective Mott Phases, and Magnetic Block States in Multiorbital Models for Iron-Based Ladders and Chains*

The discovery of superconductivity at high pressure in iron-based two-leg ladder 123 materials [1] established a new playground to better understand pairing tendencies in iron superconductors. Similarly as in Cu-oxide ladders, computational calculations using correlated electronic models can be performed with good accuracy in quasi-1D systems. Here, I will review our recent results for multiorbital Hubbard models varying the Hubbard and Hund couplings, and the electronic density. Clear indications of pair formation are found in lightly-doped ladders [2] and chains [3], and robust spin-singlet pair-pair correlations develop in those chains [3] (as in Cu-based ladders, we assume pressure leads to doping of the iron network [4]). An explanation for spin-singlet pairing based on an "orbital resonant valence bond" state is discussed for chains [5]. The magnetic properties in ladders and chains are also unexpectedly rich. An "orbital selective Mott phase" dominates in a wide range of parameters. In this regime, magnetic ``block'' states emerge, such as up-up-down-down patterns. We calculated the dynamical spin structure factor, finding a mixture of acoustic and optical modes [6] as in neutron experiments. Even more extended block states were recently discovered [7,8]. This complex behavior unveiled in models for 1D iron superconductors when studied accurately suggests that the physics of these materials could be far richer than anticipated.

[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 94, 075119 (2016)
[3] N. Patel et al., PRB 96, 024520 (2017)
[4] Y. Zhang et al., PRB 95, 115154 (2017); PRB 97, 045119 (2018)
[5] N. Patel et al., submitted
[6] J. Herbrych et al., Nat. Comm. 9, 3736 (2018)
[7] J. Herbrych et al., PRL 123, 027203 (2019)
[8] J. Herbrych et al., submitted