Dirac State Switching in Transition Metal Diarsenides*

Topological semimetals exhibiting Dirac and Weyl fermions, which support low-energy quasi-particles in condensed matter physics, have been attracting intense research interest because of the exotic properties they possess like high magnetoresistance and high carrier mobilities. The transition metal diarsenides such as MoAs₂ and WAs₂ have been reported to feature very large magnetoresistance suggesting the possibility of topological quantum state in these materials. Here, we present the systematic electronic structure measurements of TAs₂ (T = Mo, W) by using angle-resolved photoemission spectroscopy (ARPES) complemented by first-principles calculations. We observe a single Dirac surface state in MoAs₂, which switches to trivial state for different cleaving surface. Interestingly, no Dirac surface state is observed in WAs₂, despite its high magnetoresistance, highlighting the role of spin-orbit coupling in the electronic structure. Our study thus provides a new perspective on how cleavage plane and spin-orbit coupling drive changes in the electronic structures in low-symmetry systems.