  Topological semimetals feature protected nodal band degeneracies
characterized by a topological invariant known as the Chern number (C). Nodal
band crossings with linear dispersion are expected to have at most |C|=4, which
sets an upper limit to the magnitude of many topological phenomena in these
materials. Here we show that the chiral crystal PdGa displays multifold band
crossings, which are connected by exactly four surface Fermi-arcs, thus proving
that they carry the maximal Chern number magnitude of 4. By comparing two
enantiomers, we observe a reversal of their Fermi-arc velocities, which
demonstrates that the handedness of chiral crystals can be used to control the
sign of their Chern numbers.
