A semi-classical approach to electron spin resonance in quantum spin systems

We develop a semi-classical approximation to electron spin resonance in quantum spin systems, based on the rotor or non-linear sigma model. The classical time evolution is studied using molecular dynamics while random initial conditions are sampled using classical Monte Carlo methods. Although the approximation may be especially powerful in two dimensions, we apply it here to one-dimensional systems of large spin at intermediate temperatures, in the presence of staggered and uniform magnetic fields. We first test the validity of the semi-classical approximation by comparing the magnetization to quantum Monte Carlo results on S = 2 chains. Then we calculate the ESR spectrum, finding broad coexisting paramagnetic and spin wave resonances.

Reference: arXiv:1102.3239v1