ladders and chains

The discovery of superconductivity in the two-leg ladder compound BaFe₂S₃ opened a novel avenue of research because it represents the first report of pairing in a quasi-one-dimensional iron-based superconductor. Ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts. As a first step, we studied a two-orbital Hubbard model, derived from first principles, that describes individual BaFe₂S₃ ladders using the density matrix renormalization technique. We found indications of pairing between two holes in a region with orbital selective Mott phase characteristics [1]. By studying a simplified model on large systems, the two-orbital chain, we uncovered an instability toward pairing that is enhanced with increasing Hund and antiferromagnetic Heisenberg couplings. The analysis of the chain pair-pair correlations indicate that pairs form inter-orbital singlets on neighboring sites and different orbitals [2]. These results suggest that magnetic fluctuations may explain superconductivity in the iron-based ladder superconductors. Future directions of research in ladders and chains will be discussed.

[1] N. D. Patel et al., Phys. Rev. B 94, 075119 (2016)
[2] N. D. Patel et al., Phys. Rev. B 96, 024520 (2017)