Spin Dynamics of a J1-J2-K Model for the Paramagnetic Phase of Iron Pnictides

Abstract

We study the finite-temperature spin dynamics of the paramagnetic phase of iron pnictides within an antiferromagnetic J_1-J_2 Heisenberg model on a square lattice with a biquadratic coupling $-K(S_i\cdot S_j{)}^2$ between the nearest-neighbor spins. Our focus is on the paramagnetic phase in the parameter regime of this J_1-J_2-K model where the ground state is a (π,0) collinear antiferromagnet. We treat the biquadratic interaction via a Hubbard-Stratonovich decomposition, and study the resulting effective quadratic-coupling model using both modified spin wave and Schwinger boson mean-field theories; the results for the spin dynamics derived from the two methods are very similar. We show that the spectral weight of dynamical structure factor S(q,ω) is peaked at ellipses in the momentum space at low excitation energies. With increasing energy, the elliptic features expand towards the zone boundary, and gradually split into two parts, forming a pattern around (π,π). Finally, the spectral weight is anisotropic, being larger along the major axis of the ellipse than along its minor axis. These characteristics of the dynamical structure factor are consistent with the recent measurements of the inelastic neutron scattering spectra on BaFe_2As_2 and SrFe_2As_2.

13 pages, 11 figures, to be published in Phys. Rev. B

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• Magnetism in parent Fe-chalcogenides: quantum fluctuations select a plaquette order
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• Spin-state Crossover Model for the Magnetism of Iron Pnictides
• Possible Nematic Spin Liquid in Spin-$1$ Antiferromagnetic System on the Square Lattice: Implication for the Nematic Paramagnetic State of FeSe
• Temperature dependence of the paramagnetic spin excitations in BaFe${}_2$As${}_2$
• Quantum phase transitions in a spin-1 antiferromagnetic chain with long-range interactions and modulated single-ion anisotropy
• Antiferroquadrupolar order and rotational symmetry breaking in a generalized bilinear-biquadratic model on a square lattice
• Spin and quadrupolar orders in the spin-1 bilinear-biquadratic model for iron-based superconductors
• Spin fluctuation anisotropy as a probe of orbital-selective hole-electron quasiparticle excitations in detwinned Ba(Fe1-xCox)2As2
• Dynamic spin-lattice coupling and nematic fluctuations in NaFeAs
• Orbital Symmetry and Orbital Excitations in High-$T_c$ Superconductors
• Ising-nematic order in the bilinear-biquadratic model for the iron pnictides
• Density Matrix Renormalization Group Study of Nematicity in Two Dimensions: Application to a Spin-$1$ Bilinear-Biquadratic Model on the Square Lattice
• Quantum Transitions of Nematic Phases in a Spin-$1$ Bilinear-Biquadratic Model and Their Implications for FeSe
• Spin Waves and Spatially Anisotropic Exchange Interactions in the $\mathrm{S}=2$ Stripe Antiferromagnet Rb${}_{0.8}$Fe${}_{1.5}$S${}_2$
• High-Energy Damping by Particle-Hole Excitations in the Spin-Wave Spectrum of Iron-Based Superconductors
• Electron Correlation and Spin Dynamics in Iron Pnictides and Chalcogenides
• Tuning the magnetic and structural phase transitions of PrFeAsO via Fe/Ru spin dilution
• Quantum phase transition between spin liquid and spin nematics in spin-1 Kitaev honeycomb model
• Two-Fluid Description for Iron-Based Superconductors
• Magnetic and Ising quantum phase transitions in a model for isoelectronically tuned iron pnictides
• Anisotropic magnetic excitations of a frustrated bilinear-biquadratic spin model -- Implications for spin waves of detwinned iron pnictides
• Paramagnetic spin excitations in insulating Rb${}_{0.8}$Fe${}_{1.6}$Se${}_2$
• Superconducting states of a J1-J2-K model for iron pnictides
• Spin wave approach to the two-magnon Raman scattering in an J1x-J1y-J2-Jc antiferromagnetic Heisenberg model
• Unified Spin Model for Magnetic Excitations in Iron Chalcogenides
• Extension of the Lieb-Schupp theorem to the Heisenberg models with higher order interactions
• Quasi-one-dimensional spin excitations in the iron pnictide NaFe${}_{0.53}$Cu${}_{0.47}$As