Figure 4

(a) Non-radiative Q-factor \(\tt Q_{nr}\) map and (b) radiative Q-factor \(\tt Q_{r}\) map of the DSS at surface Brillouin zone, parametered in polar format with coordinates θ and φ, where Γ point is at the center (green dot) of the map and the radial direction (green arrow) away from the center represents the angle θ increasing from 2° (small green circle) to the angular position of the bulk band projection. For reference, the yellow loops denote the angular position of the NC projection, and the dot lines in (b) label the angular positions where the DSS meets the edge of the bulk band. (c) \(\tt Q_{r}\) versus θ along ГX direction (φ = 0), as denoted by the green line section in (b). The symbols are the numerically obtained \(\tt Q_{r}\), and the dash line represents the function plot \(\tt 1/\sin^{2} \theta\).