Phase Transition in a Kink and Dynamical Structure Factor of Quasi-One-Dimensional Antiferromagnets

Abstract

The dynamics of nonlinear excitations in quasi-one-dimensional magnets has been widely investigated both from the theoretical point of view and experimentally [1]. It is known that existence of solitons (kinks) in the one-dimensional systems leads to the so-called central peak (CP) in the dynamic structure factor (DSF), which determines the cross section of inelastic neutron scattering [2]. A characteristic feature of antiferromagnets (AFM), as it was shown in [3–5], is that the external magnetic field can transform the kink structure. Authors of [3–6] have considered only the stability of static kink solutions depending on the value of the external field. However, in recent works [7,8] it was found that the structure and the symmetry of moving kink and kink at rest can differ sharply. In particular this leads to kink instability at finite velocity and to phase transitions between different type of kinks [8,9]. In this paper we will show that the effects of phase transition essentially change the DSF for the case of the easy- plane (or rhombic) AFM in an external magnetic field (i. e. in the standard situation [10,11]).