Fig. 1: Our on-chip phononic crystals for SAWs.
From: Extended topological valley-locked surface acoustic waves
a Schematic of our phononic crystals containing two sets of micro-resonator pillars, marked as A and B, on a y-cut LiNbO3 semi-infinite half-space. b Unit cell of our phononic crystal, its lattice constant a = \(42/\sqrt{3}\) μm. c schematic of two inequitable pillars. d–f (upper) SEM images and (bottom) calculated band structures of three different phononic crystals with different topological phases. e A SAW Dirac “semimetal” with the same A and B pillars (rA = rB = 5.8 μm). d and f Two SAW valley “insulators” with inequivalent A/B pillars in their radius, both having omnidirectional bandgaps at their \(\bar{{{\mbox{K}}}}\) and \(\bar{{{\mbox{K}}}}\)’ points of the 1st Brillouin zones, i.e., the valleys. We call the “insulator” in d (rA = 5.9 μm rB = 3.9 μm) as valley insulator A (VA) and the “insulator” in f (rA = 3.9 μm rB = 5.9 μm) as valley insulator B (VB). Insets show the SAW flux vortices observed at their valleys.
