  Topologically protected fermionic quasiparticles appear in metals, where band
degeneracies occur at the Fermi level, dictated by the band structure topology.
While in some metals these quasiparticles are direct analogues of elementary
fermionic particles of the relativistic quantum field theory, other metals can
have symmetries that give rise to quasiparticles, fundamentally different from
those known in high-energy physics. Here we report on a new type of topological
quasiparticles -- triple point fermions -- realized in metals with symmorphic
crystal structure, which host crossings of three bands in the vicinity of the
Fermi level protected by point group symmetries. We find two topologically
different types of triple point fermions, both distinct from any other
topological quasiparticles reported to date. We provide examples of existing
materials that host triple point fermions of both types, and discuss a variety
of physical phenomena associated with these quasiparticles, such as the
occurrence of topological surface Fermi arcs, transport anomalies and
topological Lifshitz transitions.
