  We predict the existence of lateral drag forces near the flat surface of an
absorbing slab of an anisotropic material. The forces originate from the
fluctuations of the electromagnetic field, when the anisotropy axis of the
material forms a certain angle with the surface. In this situation, the spatial
spectra of the fluctuating electromagnetic fields becomes asymmetric, different
for positive and negative transverse wave vectors components. Differently from
the case of van der Waals interactions in which the forward-backward symmetry
is broken due to the particle movement or in quantum noncontact friction where
it is caused by the mutual motion of the bodies, in our case the lateral motion
results merely from the anisotropy of the slab. This new effect, of particular
significance in hyperbolic materials, could be used for the manipulation of
nanoparticles.
