Thermally Tunable Polarization-insensitive Ultra-broadband Absorber in a Terahertz Metamaterial Sustained by the Coupled Toroidal Dipole Modes

The reported terahertz (THz) metamaterial absorber (MMA) sustained by coupled toroidal dipole modes enable a distinctive path to acquire the wide-band high absorption in the multipole optical system. The coupled toroidal dipole moments existing in the toroidal metallic structure can induce the destructive and constructive interference in far- and near-field to confine the electromagnetic field, thus impelling the MMA to attain the high absorption efficiency (over 0.9) of the normally incident waves with different polarization in the spectral of 2.38{21.13 THz at 340 K, the relative absorption bandwidth (RABW) of 159.5%. In addition, owing to the characteristics of vanadium dioxide (VO2) regulated by environmental temperature, the tunability of absorption efficiency of such MMA, maximum up to 0.57 in the operating band, has been achieved through regulating the environmental temperature. The proposed method of enhancing the absorption resulting from the coupled toroidal dipole moments in a wide band can contribute to expanding the application field and the theoretical framework of multipole electrodynamics.