等离激元特异介质中的磁涡旋偶极矩及其光学相关特性

Toroidal dipole moment is the third kind of dipole moments, which is independent of the electric and magnetic dipole moments and is characterized by a vortex distribution of magnetic dipoles. This intriguing moment breaks the symmetries of both time reversal and spatial inversion, and thus is expected to exhibit various physical properties, such as dichroism, nonreciprocity, magneto-optics, and magnetoelectricity. In order to overcome the realistic disadvantage of weak optical responses of the historically neglected toroidal dipole moment in natural materials, this project will study the excitation of the toroidal dipole response and its optical-related phenomena in optical metamaterials. Thanks to the enhancement effect of plasmon resonance, it is expected that the optical characteristics of toroidal dipole moment can be observed experimentally, and thus application potentials in nano-optoelectronic functional devices can be discussed. Specifically speaking, based on our previous works, we will design novel micro-/nano-structures with optical toroidal dipolar response, and theoretically propose as well as experimentally perform investigations about the all-optical induced Hall effect in this kind of magnetically-ordered optical metamaterials by referring to previous achievements in multiferroic materials. Simultaneously, we will also analyze the cavity-related characteristics, nonreciprocal propagations, and gain-assisted characteristics associated with the magnetic-vortex resonance. This project will exhibit a series of novel optical phenomena regarding to the optical toroidal dipole moment in the metamaterial system, and consequently can provide theoretical as well as experimental results for the development of related research directions.

磁涡旋偶极矩是独立于电偶极矩、磁偶极矩之外的第三类偶极矩，以磁偶极的涡旋分布为特征。它同时打破时间和空间反演对称性，具有二向色性、非互易性、磁光、磁电等众多物理特性。为弥补自然界物质中磁涡旋偶极响应非常微弱、长期以来未被重视的现状，本项目拟研究光波段特异介质体系中该类偶极矩响应的激发及其产生的光学现象。借助于等离激元的共振增强效应，可望从实验上揭示该体系中磁涡旋偶极矩相关的光学特征，并分析其在纳光电功能器件方面的应用前景。具体来说，在前期工作的基础上，我们将优化设计出独特的光学磁涡旋微纳结构，并结合多铁材料中磁涡旋偶极矩的研究成果，理论上提出、实验上验证此类磁有序特异介质中全光诱导的霍尔效应。同时，还将分析所设计的特异介质中磁涡旋偶极共振的光学谐振腔、非互易传输以及增益等光学特性。本项目将揭示特异介质体系中磁涡旋偶极矩的一系列新颖光学现象，为相关方向的发展提供一定的理论结果和实验依据。

光波段磁涡旋偶极共振增强响应是当前等离激元特异介质领域具有重要学术价值和应用背景的研究方向之一，可以促进人们认识自然界中(如基本粒子、多铁材料)磁涡旋偶极相关特性、拓展新型光磁相关的微纳光子学功能器件。本项目中，我们执行了纳米结构等离激元特异介质的理论设计、数值仿真、纳米加工、光学测量等一系列研究工作，建立了纳光子平台、培养了科研队伍、实现了预期的各项研究目标。例如，1)我们仿真设计、实验加工、光学测量了V型圆槽中光波磁涡旋偶极响应的角度分辨反射谱；2)理论和仿真研究了基于光波磁涡旋偶极共振响应的电磁场局域特征，在此基础上分析了光力增强效应与环状俘获纳米粒子效应；3)通过设计深度不对称的圆环槽等新型特异介质，实现了基于磁涡旋偶极模式的红外光完美吸收效应、增益辅助的定向辐射增强效应、等离激元诱导透明效应等。另外，我们设计了一种具有反键态磁序特征的椭圆环纳米结构特异介质，研究了光子自旋角动量与该结构等离激元模式的轨道角动量相互耦合后产生的光子自旋霍尔效应。我们还研究了磁性材料辅助的增益/损耗共轭平衡的波导系统中单向性光学非互易传输。与这种非互易传输类比，我们通过直线折叠而成的Omega纳米结构，设计了具有手性特征的双层Omega特异材料，获得了高效的红外波段正交偏振转化，实现了具有单向传输特性的不对称透射。已在Appl. Phys. Lett., Opt. Express，Opt. Lett.，Phys. Rev. B等刊物上发表SCI论文16篇，申请并获得国家发明专利2项，培养研究生5名（另有6名在读）。上述工作为课题组今后纳米光子学相关的研究提供了良好的驱动力，其中发现的新颖光学现象对微纳光子学领域的相关研究，特别是有关光波段磁涡旋偶极响应的探索有一定的学术价值和促进作用，对设计相关功能的微纳光子器件也具有一定的借鉴意义。