Tuning the magnetic toroidal dipole response in dielectric metasurfaces

A toroidal dipole is a fundamental electromagnetic excitation independent of electric and magnetic dipoles. At present, a great deal of attention has been paid to the characteristics and applications of electric toroidal dipole resonance, while investigation of magnetic toroidal dipole (MTD) resonance is limited. The dielectric metasurface provides a good platform for the excitation of MTD. In this work, we numerically study the MTD response on a silicon tetramer metasurface. The near-field distribution and multipole decomposition fully confirm that the MTD dominates the resonance mode. Also, by integrating the phase-change material G e 2 S b 2 T e 5 film onto this metasurface, the modulation properties of relative transmission, MTD far-field scattering, phase, and local electric and magnetic fields of this hybrid device are effectively studied. The maximum modulation depth of transmission reaches 88%, which is attributed to the strong resonance of MTD. Our work provides a route for the achievement of actively tunable optical nano-devices.