Asymmetric Elastic Bound State in the Continuum by an Exceptional Point
Liyun Cao, Badreddine Assouar
Abstract
In this Letter, we experimentally and theoretically demonstrate an asymmetric elastic bound state in the continuum (BIC) induced by an exceptional point (EP) in an open elastic system. For positive incidence, the characteristic vanishing linewidth of a BIC is observed, whereas it is absent for negative incidence. Notably, the resulting nontrivial quasi-BIC (qBIC) exhibits perfect energy localization and extremely high quality factors (Q), while for the negative direction, most of the energy is radiated, yielding Q close to zero. By modulating the system's loss, this nontrivial qBIC mode can approximately evolve into a genuine BIC. Remarkably, the nontrivial mode can also coalesce into an EP BIC, where the energy is entirely localized within the non-Hermitian resonator system with asymmetric loss. Our Letter establishes a nontrivial connection between two seemingly unrelated concepts-BICs and EPs-and reveals a novel physical mechanism for achieving asymmetric high Q and strong energy localization, offering new opportunities for high-performance elastic-wave devices.