  A general phenomenon of the Cherenkov radiation known in optics or acoustics
of conventional materials is a formation of a forward cone of, respectively,
photons or phonons emitted by a particle accelerated above the speed of light
or sound in those materials. Here we suggest three-dimensional topological
insulators as a unique platform to fundamentally explore and practically
exploit the acoustic aspect of the Cherenkov effect. We demonstrate that
applying an in-plane magnetic field to a surface of a three-dimensional
topological insulator one may suppress the forward Cherenkov sound up to zero
at a critical magnetic field. Above the critical field the Cherenkov sound
acquires pure backward nature with the polar distribution differing from the
forward one generated below the critical field. Potential applications of this
asymmetric Cherenkov reverse are in design of low energy electronic devices
such as acoustic ratchets or, in general, in low power design of electronic
circuits with a magnetic field control of the direction and magnitude of the
Cherenkov dissipation.
