Research On Magnetic Fano Resonance In Silver Nanostructures

The interaction between metal nanoparticle and subwavelength incident light can generate hybridized plasmon modes when the incident light frequency is the same as the free electron oscillation frequency.The plasmon resonance is sensitive to the changing of the surrounding medium,the direction of the incident light,the material of the structure and the shape of the nanostructure.The position and intensity of the resonance peak can be adjusted by these adjustments.Based on the above novel optical properties,plasmon resonance has great research value of surface plasmon enhanced,plasmonic Fano switch,solar battery and transmission waveguide anetc.The complex nanostructures are designed,such as the ring-disk nanocavities and the asymmetrical dual-nanoellipsoid in the cavity of the ring,which can be achieved multiple Fano resonance.Based on the research status of surface plasmon resonance,Fano line shapes can't be effective regulated and the lack of regulation of magnetic resonance is not comprehensive.We design a nonconcentric asymmetric ring-ring and double split ring/square ring to study the the optical properties of the structures.The main contents of this paper are divided into thwo parts:In the first of this letter,we have systemmatically investigated the optical properties of the nonconcentric asymmetric ring-ring(NARR).The magnetic Fano resonances is not excited in concentric symmetric ring-ring.For the symmetry breaking of the structure,mutipolar higher order magnetic Fano resonances can be excited,which can be manipulated by adjusting the offset of the cavity,the width of the outer ring and the magnification times of the structure.The magnetic resonances can be suppressed by tuning the offset of the inner ring.The optical properties of the plasmonic nanostructure can be applied in magnetic Fano switch and multi-wavelength surface enhanced spectroscopy.In the second of this letter,double split ring/square ring(DSR/SR)is investigated.Anti-bonding and bonding modes are excited in the extinction cross section of the structure.The magnetic resonances have closed current and generate magnetic Fano resonances.The electric resonances generate electric Fano resonances without closed current.In order to effectively adjust the Fano resonance,the gap,the position and intensity of the Fano resonance is adjusted by changing the gap,the width of opening and the magnification times of the structure are changed when the structure of the system is symmetrical.Furthermore,the magnetic Fano resonances have even current loops and the adjacent current loops are in antiphase.In order to excite the four and eight closed currents,the structure symmetry is broken by changing the arm length and the offsets of square ring.The magnetic field enhancement of new magnetic resonance reaches 30.4,which can be applied in surface enhanced spectroscopy.Finally,the FOM and the sensitivity of modes are calculated.The quality factor of magnetic resonance is the largest,which attains 25.3.Different magnetic resonances are sensitive to refractive index of the surrounding environment.This feature can be applied in sensing.