Non-Hermitian analysis of surface creeping waves in optical microcavities: Nature of external resonances

Undiscovered properties of surface creeping wave states given by complex angular momentum poles, so-called Regge poles (RPs) in optical microcavity scattering, are transparently elucidated on the frameworks of non-Hermitian physics. In particular, we analytically show that the nature of external resonances (ERs) given by complex wave numbers is equivalent to surface creeping wave RPs. Moreover, by obtaining the full structural characteristics of RPs for different polarizations, it is found that notable nontrivial RPs in transverse-magnetic polarization arise owing to the classical Brewster angle. Finally, we explicitly demonstrate the emergence of non-Hermitian degeneracies incorporating different classes of RPs.