  We present a semiclassical explanation for the morphology of the surface
Fermi arcs of Weyl semimetals. Viewing the surface states as a two-dimensional
Fermi gas subject to band bending and Berry curvatures, we show that it is the
non-parallelism between the velocity and the momentum that gives rise to the
spiral structure of Fermi arcs. We map out the Fermi arcs from the velocity
field for a single Weyl point and a lattice with two Weyl points. We also
investigate the surface magnetoplasma of Dirac semimetals in a magnetic field,
and find that the drift motion, the chiral magnetic effect and the
Imbert-Fedorov shift are all involved in the formation of surface Fermi arcs.
Our work not only provides an insightful perspective on the surface Fermi arcs
and a practical way to find the surface dispersion, but also paves the way for
the study of other physical properties of the surface states of topological
semimetals, such as transport properties and orbital magnetization, using
semiclassical methods.
