Frequency dependence of resonance in one-dimensional antiferromagnetic Heisenberg chain

Abstract

This chapter discusses Heisenberg anti-ferromagnetic spin systems with isotropic g-tensor, where only anisotropic spin interaction such as the dipole interaction violates the SU(2)—that is, the Heisenberg symmetry—and causes other resonant peaks than the paramagnetic resonance (PMR). The chapter investigates the origin in which the resonant field shifts form paramagnetic resonance field by studying the change that occurs in the energy structure. Electron spin resonance (ESR) in S = 1/2 spin system is studied by a direct numerical method calculating the dynamical susceptibility expressed by the Kubo formula. The chapter explored qualitatively the different frequency-dependence of the resonant shift at various temperatures—namely, the qualitatively different behavior of the temperature-dependence of that at various frequencies. From the results at lower temperatures, it is expected that ESR can be a fine method to investigate the ground state of the material.