Browsing by Author "Ergueta, Patricia Bilbao"
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Item Ising-nematic order in the bilinear-biquadratic model for the iron pnictides(American Physical Society, 2015) Ergueta, Patricia Bilbao; Nevidomskyy, Andriy H.Motivated by the recent inelastic neutron scattering (INS) measurements in the iron pnictides which show a strong anisotropy of spin excitations even above the magnetic transition temperature TN, we study the spin dynamics within the frustrated Heisenberg model with biquadratic spin-spin exchange interactions. Using the Dyson-Maleev (DM) representation, which proves appropriate for all temperature regimes, we find that the spin-spin dynamical structure factors are in excellent agreement with experiment, exhibiting breaking of the C4 symmetry even into the paramagnetic region TNItem Unified spin model for magnetic excitations in iron chalcogenides(American Physical Society, 2017) Ergueta, Patricia Bilbao; Hu, Wen-Jun; Nevidomskyy, Andriy H.Recent inelastic neutron scattering (INS) measurements on FeSe and Fe(Te1−xSex) have sparked intense debate over the nature of the ground state in these materials. Here we propose an effective bilinear-biquadratic spin model, which is shown to consistently describe the evolution of low-energy spin excitations in FeSe, both under applied pressure and upon Se/Te substitution. The phase diagram, studied using a combination of variational mean-field, flavor-wave calculations and density-matrix renormalization group (DMRG), exhibits a sequence of transitions between the columnar antiferromagnet common to the iron pnictides, the nonmagnetic ferroquadrupolar phase attributed to FeSe, and the double-stripe antiferromagnetic order known to exist in Fe1+yTe. The calculated spin structure factor in these phases mimics closely that observed with INS in the Fe(Te1−xSex) series. In addition to the experimentally established phases, the possibility of incommensurate magnetic order is also predicted.