  A switchable hyperbolic material (SHM) is investigated, with which one can
turn on or off the hyperbolic dispersion of the material via magnetic control.
The SHM has simple structure, with a one-dimensional periodic stacking of
dielectric layer and gyromagnetic layer. The hyperbolic dispersion of SHM is
due to the negative effective permeability of gyromagnetic layers, and it can
be transformed into a regular circular dispersion when the d.c. magnetic field
is switched off. This switchable dispersion transition is reversible, which may
have great potential applications in many fields.
