Magnetic properties and pairing tendencies of the iron-based superconducting ladderBaFe2S3: Combinedab initioand density matrix renormalization group study

Abstract

The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3 [H. Takahashi et al., Nature Materials 14, 1008] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasi one-dimensional iron-based high critical temperature superconductor. Similarly as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In this publication, we derive a twoorbital Hubbard model from first principles that describes individual ladders of BaFe2S3. The model is studied with the density matrix renormalization group. These first reported results are exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; (ii) with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system. In addition, orbital selective Mott phase characteristics develop with doping, with only one Wannier orbital receiving the hole carriers while the other remains half-filled. These results suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies and other exotic properties of iron-based high critical temperature superconductors in general.

Pairing tendencies in a two-orbital Hubbard model in one dimension

“…However, the issue of pairing was more challenging due to severe size restrictions. In [31] it was assumed that high pressure causes doping of the two-leg ladders, a result supported by recent density functional theory calculations [33], and in agreement with the Cu-oxide two-leg ladders context where experiments showed [34] that indeed pressure transfers charge away from the ladders into chains effectively doping them. Under these assumptions an intriguing result was unveiled: using 2×8 clusters indications of binding of two holes were observed at intermediate values of the on-site Hubbard U repulsion, and for a realistic Hund coupling J H /U = 0.25.…”

“…Under these assumptions an intriguing result was unveiled: using 2×8 clusters indications of binding of two holes were observed at intermediate values of the on-site Hubbard U repulsion, and for a realistic Hund coupling J H /U = 0.25. Note that this binding does not occur at small U , so in principle it is outside the range of weak coupling expansions, and also does not occur in very strong coupling [31]. Remarkably, the reported binding happens in a finite and intriguing range of U/W , where W is the electronic bandwidth.…”

“…The reason is that multiorbital Hubbard models are needed and even powerful techniques such as the Density Matrix Renormalization Group (DMRG) [30] have difficulty in reaching sufficient accuracy for conclusive results. In spite of these limitations, a recent publication [31] reported progress in the study of a twoorbital model for BaFe 2 S 3 . In particular, the magnetic order with FM rungs and AFM legs was qualitatively understood and clearly reproduced over robust portions of parameter space [32].…”

Pressure-driven phase transition from antiferromagnetic semiconductor to nonmagnetic metal in the two-leg ladders AFe2X3 ( A=Ba,K

“…However, recently iron chalcogenides with a different structure, the so-called 123-type AFe 2 X 3 (A=K, Cs, Rb, or Ba; and X=S, Se, or Te), have drawn considerable attention [20][21][22][23][24][25][26][27]. These materials display unique quasi-one-dimensional two-leg ladder iron structures (see Fig.…”

Magnetic excitation spectra of strongly correlated quasi-one-dimensional systems: Heisenberg versus Hubbard-like behavior

“…11 Spin ladders have applications ranging from high-temperature superconductors [12][13][14][15] to ultracold atoms. 16,17 Recently, unusual and intriguing physical phenomena were observed in spin systems, such as the Bose-Einstein condensation of magnons, 18 the fractionalization of spin excitations, 19,20 spinon attraction, 21 and unusual disorder effects.…”