2006/02/23 by Hosho Katsura, Alexander V. Balatsky, Naoto Nagaosa · 1 citation
Physics and Astronomy · #cond-mat.str-el
paper · pdf · doi:10.1103/physrevlett.98.027203
published as Phys. Rev. Lett. 98, 027203 (2007) · 5 pages, 1 figure
arxiv created 2006/02/23 · arxiv updated 2009/12/01
Collective mode dynamics of the helical magnets coupled to electric polarization via spin-orbit interaction is studied theoretically. The soft modes associated with the ferroelectricity are not the transverse optical phonons, as expected from the Lyddane-Sachs-Teller relation, but are the spin waves hybridized with the electric polarization. This leads to the Drude-like dielectric function ε(ω) in the limit of zero magnetic anisotropy. There are two more low-lying modes; phason of the spiral and rotation of helical plane along the polarization axis. The roles of these soft modes in the neutron scattering and antiferromagnetic resonance are revealed, and a novel experiment to detect the dynamical magneto-electric coupling is proposed.