Unusual spin and angular momentum of Dyakonov waves at the hyperbolic-material surface

Three Dyakonov-like polaritons (DLPs) exist at the interface between a hyperbolic material (HM) and a covering medium (CM). Each DLP is a hybridized-polarization surface polariton composed of two evanescent waves on both sides of the interface. We investigated their spin and angular momentum. We analytically found that any DLP carries two spins producing mutually orthogonal spin angular-momentum (SAM) components. The spins and angular-momentum have different features on both sides of the interface, and further differences among the three DLPs are very obvious. For the interface structure formed by hexagonal boron nitride (hBN) and air, the SAM mainly distributes in the air for DLP-I, the SAM is approximately transverse to the propagating direction for DLP-II, and it is surprisingly large in the hBN for DLP-III and can reach several ten times that in the usual situation. There is the spin-k locking for every DLP, but the spin-k locking is different for different DLPs. These properties do not exist for traditional surface polaritons or ordinary evanescent waves. The above unique results can support some potential applications in the fields of nano- and micro-photonics, optoelectronics and mechanics, as well as relevant technologies.