Fig. 2
From: Active control of anapole states by structuring the phase-change alloy Ge2Sb2Te5
Broadband tuning and shifting of the multipolar scattering states in GST spheres. a Scattering efficiency Qscat of a single GST sphere with a fixed radius R = 450 nm and varying crystallinities C. Two white dashed lines indicate the scattering maxima and minima corresponding to the ED and anapole states. b Analytically solved ED and anapole conditions. Shifting between these two states can be realized within an ultrabroad bandwidth over 700 nm (the gray shaded area) by exploiting the intermediate levels of GST spheres. c Scattering cross-sectional contrast between aGST and 25%-cGST spheres with varying radii R. Three white dashed lines show the most noticeable scattering contrasts. d Analytically solved MD, ED, and anapole conditions to account for the scattering contrast between the aGST and 25%c-GST spheres. The ED and anapole positions are almost perfectly overlapped in a wavelength range spanning around 1.5 μm
