  Recent advances in engineered material technologies (e.g., photonic crystals,
metamaterials, plasmonics, etc) provide valuable tools to control Cherenkov
radiation. In all these approaches, however, the designed materials interact
only with the particle velocity to affect Cherenkov radiation, while the
influence of the particle trajectory is generally negligible. Here, we report
on surface Dyakonov-Cherenkov radiation, i.e. the emission of directional
Dyakonov surface waves from a swift charged particle moving atop a birefringent
crystal. This new type of Cherenkov radiation is highly susceptible to both the
particle velocity and trajectory, e.g. we observe a sharp radiation enhancement
when the particle trajectory falls in the vicinity of a particular direction.
Moreover, close to the Cherenkov threshold, such a radiation enhancement can be
orders of magnitude higher than that obtained in traditional Cherenkov
detectors. These distinct properties allow us to determine simultaneously the
magnitude and direction of particle velocities on a compact platform. The
surface Dyakonov-Cherenkov radiation studied in this work not only adds a new
degree of freedom for particle identification, but also provides an
all-dielectric route to construct compact Cherenkov detectors with enhanced
sensitivity.
