Observation of Gapless Dirac Surface States in ZrGeTe*

The experimental discovery of the topological Dirac semimetal provides a platform to search for novel exotic quantum phases in real materials. Recently, ZrSiS-type materials have been established as topological nodal-line semimetals where gapped Dirac-like surface states are observed. Here, we present an angle-resolved photoemission spectroscopy (ARPES) study of ZrGeTe, a non-symmorphic symmetry protected Dirac semimetal. We observe two Dirac-like gapless surface states at the same X point of the Brillouin zone. Our theoretical analysis and first-principles calculations reveal that these are protected by crystalline symmetry. Hence, ZrGeTe appears as a unique example of a naturally fine tuned system where the interplay between symmorphic and non-symmorphic symmetry leads to rich phenomenology, and thus opens opportunities to investigate the physics of Dirac semimetallic and topological insulating phases realized in a single material.