Insights into the Stability and Surface Termination of Topological Semimetal NbAs₂

NbAs2, a topological semimetal, has stirred considerable interest for its potential usage in magnetic and fault-tolerant quantum computation superconductor devices, owing to its superconductivity, enormous magnetoresistance, and anisotropic magneto-transport attributes. Yet, its environmental stability, a crucial factor for practical applications, remains largely unexplored. Herein, a comprehensive examination of the stability and electronic properties of the (001) surface of NbAs2 utilizing density functional theory (DFT) and surface science experiments is conducted. The theoretical deductions reveal that As atoms, organized in a buckled honeycomb configuration, terminate the bare (001) surface, akin to the tensile blue arsenene monolayer along the armchair direction. This study further demonstrates that the oxidation barrier is particularly low (only 0.2 eV), highlighting that the (001) surface is highly prone to oxidation under standard conditions, forming a As2O5+Nb2O5/NbAs2 heterostructure. Additionally, it observes that oxidation adversely affects the electronic characteristics of the topological semimetal NbAs2. The conclusions underscore the need for NbAs2 to be managed under high vacuum conditions or to be encapsulated for any usage in the ambient atmosphere in order to retain its electronic properties for practical purposes.