Fig. 3: Topological quadratic surface states on the (001) surface of the 3D PTI.
From: Three-dimensional photonic topological insulator without spin–orbit coupling
a, b Measured (a) and simulated (b) surface dispersions. Gray areas represent the projected bulk bands and blue curves denote surface states localized at the top surface. Black lines indicate the light cone. c Simulated surface dispersion in the (001) surface BZ. d Measured (top) and simulated (bottom) isofrequency contours of the surface states at 6.59, 6.76, and 7.09 GHz. e Spectral flow of the Zak phases. Inset shows the 3D BZ with a family of C4-invariant loops, along which the Zak phases are calculated. The Zak phase diagram proves the nontrivial ℤ2 topological invariant, v0 = 1.
