Effect of spin-orbit coupling on formation of native defects in Weyl fermion semimetals: The case of TX (T=Ta,Nb ; X=As,P)

Abstract

How to control the formation of native defects is crucial to obtaining high-quality samples and realizing the balance between electrons and holes for achieving high carrier mobilities in noncentrosymmetric Weyl fermion semimetals (WSMs). Using first-principles calculations, we explore the formation mechanisms of native defects in the family of $TX$ ($T=\text{Ta}$, Nb; $X=\text{As}$, P), and find that the spin-orbit coupling (SOC) is not only intrinsic to these semimetals but also plays a significant role in dictating the formation of native defects. The calculated defect formation energies with the SOC are lower than those without the SOC. The detailed analyses of partial density of states reveal that the valence shells of $T$--$d$ and $X$--$p$ hybridization states contribute to the antibonding states in $TX$ compounds. The broadness of $T$--$d$ and $X$--$4p$ hybridization states with the SOC inclusion increases by about 1 eV compared with the corresponding $TX$ without the SOC consideration. The more delocalized $T$--$d$ and $X$--$p$ hybridization states increase the energy of antibonding states and further attribute to the stabilization of native defects with the reduced formation energies in $TX$ compounds. We also estimate the defect concentrations based on our accurately calculated formation energies of native defects, and propose practical strategies to control their concentrations to grow high-quality samples. Our results provide insights to the defect behavior under the effect of the SOC in WSMs.