1] Department of Physics, Budapest University of Technology and Economics, Budapest 1111, Hungary [2] Condensed Matter Research Group of the Hungarian Academy of Sciences, Budapest 1111, Hungary.
Department of Physics, Budapest University of Technology and Economics, Budapest 1111, Hungary.
Nat Commun. 2014;5:3203. doi: 10.1038/ncomms4203.
The coupling between spins and electric dipoles governs magnetoelectric phenomena in multiferroics. The dynamical magnetoelectric effect, which is an inherent attribute of the spin excitations in multiferroics, drastically changes the optical properties of these compounds compared with conventional materials where light-matter interaction is expressed only by the dielectric permittivity or magnetic permeability. Here we show via polarized terahertz spectroscopy studies on multiferroic Ca2CoSi2O7, Sr2CoSi2O7 and Ba2CoGe2O7 that such magnetoeletric spin excitations exhibit quadrochroism, that is, they have different colours for all the four combinations of the two propagation directions (forward or backward) and the two orthogonal polarizations of a light beam. We demonstrate that one-way transparency can be realized for spin-wave excitations with sufficiently strong optical magnetoelectric effect. Furthermore, the transparent and absorbing directions of light propagation can be reversed by external magnetic fields. This magnetically controlled optical-diode function of magnetoelectric multiferroics may open a new horizon in photonics.
自旋和电偶极子的耦合控制着多铁体中的磁电现象。与传统材料相比，多铁体中的动态磁电效应是其自旋激发的固有属性，这极大地改变了这些化合物的光学性质，在传统材料中，光与物质的相互作用仅由介电常数或磁导率表示。在这里，我们通过对多铁体 Ca2CoSi2O7、Sr2CoSi2O7 和 Ba2CoGe2O7 的极化太赫兹光谱研究表明，这种磁电自旋激发表现出四色性，即对于光束的两个传播方向（前向或后向）和两个正交偏振的所有四种组合，它们都具有不同的颜色。我们证明，对于具有足够强的光电磁效应的自旋波激发，可以实现单向透明。此外，光传播的透明和吸收方向可以通过外部磁场反转。这种磁电多铁体的磁控光学二极管功能可能为光子学开辟一个新的领域。
