  We predict here that a slab made of a doped semiconductor can exhibit
anomalous refraction under the application of a static magnetic field. This
anomalous refraction takes place in the far-infrared range and it occurs for
any angle of incidence. We show that this effect is due to the fact that a
doped semiconductor under a magnetic field can behave, to some extent, as a
hyperbolic metamaterial. We also show that the occurrence of this anomalous
refraction enables a semiconductor slab under a magnetic field to partially
focus the electromagnetic radiation. The remarkable thing in our case is that
we deal with naturally occurring materials and the anomalous refraction can be
tuned at will with an external field.
