“It’s like tossing a stone into a still pond and seeing the ripples remain motionless, vibrating only in place. Even though the system allows wave motion, the energy doesn’t spread—it stays perfectly confined,” Yeongtae Jang, lead researcher and a PhD student at Pohang University of Science & Technology (POSTECH), said.

The individually confined wave modes (BIC and flat band) collectively form a non-spreading band across a system, called Bound Band in the Continuum (BBIC). This special wave behavior keeps the energy trapped even when the wave moves through a connected system.