Magnetic excitations in quasi-one-dimensional helimagnets: Magnon decays and influence of interchain interactions

Article

关键词: HEISENBERG-ANTIFERROMAGNET;    SQUARE-LATTICE;    SPIN;   

DOI  :  10.1103/PhysRevB.94.134416

来源: SCIE

【 摘 要 】

We present a comprehensive study of the magnetic properties of the long-range-ordered quasi-one-dimensional J(1)-J(2) systems with a newly developed torque equilibrium spin-wave expansion approach, which can describe the spin Casimir and magnon decay effects in a unified framework. While the framework does not lose generality, our discussion will be restricted to two representative systems, each of which has only one type of interchain coupling (J(3) or J(4)) and is referred to as the J(3) or J(4) system, respectively. In spite of the long-range spiral order, the dynamical properties of these systems turn out to be highly nontrivial due to the incommensurate noncollinear spin configuration and the strong quantum fluctuation effects enhanced by the frustration and low dimensionality. Both the systems show prominent spin Casimir effects induced by the vacuum fluctuation of the spin waves and related modification of the ordering vector, Lifshitz point position, and sublattice magnetization. In addition to these static properties, the dynamical behaviors of these systems are also remarkable. Significant and spontaneous magnon decay effects are manifested in the quantum corrections to the excitation spectrum, including the broadening of the spectrum linewidth and downward renormalization of the excitation energy. Furthermore, the excitation spectrum appears to be very sensitive to the types of the interchain coupling and manifests three distinct features: (i) the magnon decay patterns between the J(3) and J(4) systems are very different, (ii) the renormalized spectrum and the overall decay rate of the J(3) and J(4) systems show very different sensitivity to the magnetic anisotropy, and (iii) there is a nearly flat mode in the renormalized magnon spectrum of the J(4) system along the X-M direction. By adjusting the strength of magnetic anisotropy and varying the approximation scheme, it is revealed that these striking distinct features are quite robust and have deep connection with both the spin Casimir and the magnon decay effects. Thus these special consequences of the interchain coupling on the spin-wave dynamics may serve as a set of probes for different types of interchain couplings in experiments. Finally, to guide experimental measurements such as inelastic neutron scattering in realistic materials and complement our theoretical framework, we develop an analytical theory of the dynamical structure factor within the torque equilibrium formulism and provide explicit results of the quasi-one-dimensional J(1)-J(2) systems.

【 授权许可】

Free