Termination Dependent Topological Surface States in Nodal Loop Semimetal HfP2*

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 nodal line type features in respect to spin orbit coupling. Additionally, The surface environment of a material can severely impact the surface states that are probed by angle resolved photoemission spectroscopy (ARPES). For the first time, we report the experimental observation of topological surface states in the nodal loop semimetal HfP2 using ARPES which is supported by our first principles calculations. Our study shows termination dependent surface states in this compound which are linked to three unique nodal loops that are confirmed 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.