Spin Dynamics of a $J_1-J_2$ Antiferromagnet and its Implications for Iron Pnictides

TL;DR

This paper investigates the finite-temperature spin dynamics of a $J_1-J_2$ antiferromagnet using modified spin wave theory, revealing anisotropic correlations and elliptic features in the dynamical structure factor relevant to iron pnictides.

Contribution

It provides a detailed analysis of spin dynamics in the paramagnetic phase of a $J_1-J_2$ model, highlighting anisotropic correlations and their experimental implications.

Findings

Identification of short-range anisotropic antiferromagnetic correlations

Elliptic features in the dynamical structure factor

Variation of spin dynamics with temperature and energy

Abstract

Motivated by the recent observation of antiferromagnetic correlations in the paramagnetic phase of iron pnictides, we study the finite-temperature spin dynamics of a two-dimensional $J_1-J_2$ antiferromagnet. We consider the paramagnetic phase in the $J_2>J_1$ regime of a $(\pi,0)$ collinear ground state, using the modified spin wave theory. Below the mean-field Ising transition temperature, we identify short-range anisotropic antiferromagnetic correlations. We show that the dynamical structure factor $\mathcal{S}(\mathbf{q},\omega)$ contains elliptic features in the momentum space, and determine its variation with temperature and energy. Implications for the spin-dynamical experiments in the iron pnictides are discussed.