  Symmetry plays a major role in all disciplines of physics. Within the field
of topological materials there is a great interest in understanding how the
mechanics of crystalline and internal symmetries protect crossings between the
conduction and valence bands. Additionally, exploring this direction can lead
to a deeper understanding on the topological properties of crystals hosting a
variety of symmetries. For the first time, we report the experimental
observation of topological surface states in the nodal loop semimetal HfP2
using angle resolved photoemission spectroscopy (ARPES) which is supported by
our first principles calculations. Our study shows termination dependent
surface states in this compound. Our experimental data reveal surface states
linked to three unique nodal loops confirmed by theoretical calculation to be
topologically non-trivial. This work demonstrates that transition metal
dipnictides provide a good platform to study non-trivial topological states
protected by nonsymmorphic symmetry.
