Progress in 3D ring magnetic resonance metamaterials with high quality factors in China

    The toroidal moment is an electromagnetic excitation generated by a current flowing along a warp of a torus or a magnetic dipole moment connected end to end. Due to its weak strength, it is often obscured by the electrode moment and the magnetic moment. It is difficult to be directly observed. Until 2010, people used the metamaterial structure to achieve the electromagnetic response dominated by the dynamic ring magnetic moment in the microwave band. The dynamic ring magnetic moment has extraordinary locality and radiation suppression capability of electromagnetic energy. Therefore, the ring magnetic moment of high quality factor has important application value in the fields of plasmon laser, sensing, optical rotation and negative refractive index. However, in the high-frequency band, due to the limitation of material structure and spatial modulation capability, it is still difficult to realize the practical magnetic ring moment resonance super material.  

    In recent years, the Institute of Physics of the Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics (micro-processing) has been working on the processing methods and device applications of 3D micro-nanostructures. They invented a new method based on focused ion beam for strain-induced 3D micro-nanostructure processing, which can perform multi-dimensional and orderly folding of 1D and 2D materials to achieve the spatial, size, period and geometry of nanostructured elements. Large area controllable processing that can be modulated.  

    Recently, the laboratory Dr. Liu Zhe and researchers Li Junjie and Gu Changzhi and others extended this folded 3D structure material from metal nanowires and nanofilms to metal/dielectric composite structures, using transparent SiNx films as the backbone, using focused ion beams. The strain-induced folding process combines micron-sized metal open resonant ring structures in different opening directions and spatial positions in 3D space to obtain 3D optical metamaterials with high configuration degrees of freedom. Under the excitation of the incident light in the vertical direction, the metal resonance ring generates LC resonance, and the resonance modes of the resonance rings in different opening directions are coupled, resulting in a magnetic couple.

    The polar moments meet end to end in a ring shape to form a ring magnetic dipole resonance. The ring magnetic resonance is located in the mid-infrared band and has a quality factor of up to 20.78, which is the highest value reported in the optical band.

          By analyzing the radiant energy spectrum of the magnetic dipole moment, they observed that the maximum value of TZ at the resonance frequency proves the existence of the ring magnetic dipole resonance. In order to make the intensity of the ring magnetic dipole radiation higher than that of the electric dipole and the magnetic dipole, they use the obliquely incident TM wave to excite and find that as the incident angle increases, the TZ radiation component gradually increases, and at the incident angle of 75° Its radiation intensity exceeds the electric dipole and magnetic dipole while still maintaining a high quality factor. This result demonstrates the possibility of using a folded 3D structure to achieve high quality factor ring magnetic dipole resonance, showing broad application prospects in the fields of high performance sensing and plasmon laser.