Goos-Hänchen shift in an ENZ structure with quasi-bound states in the continuum

Exceptional points and bound states in the continuum are unique singularities of non-Hermitian systems, which have received enormous interest recently. However, the behavior of the Goos-Hänchen shift at these singularities in a structure containing parity-time symmetric epsilon near-zero material remained elusive. In this work, we utilize balanced gain and loss epsilon near-zero layers separated by a spacer for the investigation of the Goos-Hänchen shift. We demonstrate that a giant Goos-Hänchen shift can arise near the quasi-bound state in a continuum. The quasi-BIC in such structures can be tuned with the incident frequency, angle, and the gain-loss contrast, which directly results in tuning the Goos-Hänchen shift. The enhancement of the longitudinal displacement is governed by the abrupt phase change at the quasi-BIC. Our results shed light on the Goos-Hänchen shift of light and might find potential applications in refractive index sensing.