Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2011-10-04
Phys. Rev. B 85, 094410 (2012)
Physics
Condensed Matter
Strongly Correlated Electrons
8 pages, 7 figures. v2: significantly expanded
Scientific paper
10.1103/PhysRevB.85.094410
We study a two-orbital spin model to describe (pi,0) stripe antiferromagnetism in the iron pnictides. The "double-spin" model has an on-site Hunds's coupling and inter-site interactions extending to second neighbors (inter- and intra-orbital) on the square lattice. Using a variational method based on a cluster decomposition, we optimize wave functions with up to 8 cluster sites (up to 2^16 variational parameters). We focus on the anomalously small ordered moments in the stripe state of the pnictides. To account for it, and large variations among different compounds, we show that the second-neighbor cross-orbital exchange constant should be ferromagnetic, which leads to "partially hidden" stripe order, with a moment that can be varied over a large range by small changes in the coupling constants. In a different parameter region, we confirm the existence of a canted state previously found in spin-wave theory. We also identify several other phases of the model.
Liu Chan Chiang
Sandvik Anders. W.
Yao Dao-Xin
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