Electronic structure of the antiferromagnetic topological insulator candidate GdBiPt

We studied the electronic structures of antiferromagnetic (AFM) GdBiPt with propagating vectors Q1= (0,0,[pi]) (A-type) and Q2=([pi],[pi],[pi]) (G-type) by performing first-principles calculation based on density-functional theory with modified Becke and Johnson local-density approximation potentials plus Hubbard U (MBJLDA+U). With the total energy calculation, the G-type AFM spin-ordered state is relatively more stable than the A-type AFM spin-ordered state, although the difference in total energy is minute. Our band-structure calculation predicts that the A-type AFM state is topologically nontrivial due to a single s-character band inversion at the [Gamma] point, which is similar to the band inversions in half-Heusler topological insulator candidates and bulk HgTe semiconductors, while the G-type AFM state is topologically trivial due to the absence of s/p band inversion. With a realistic tight-binding model calculation with 20 bands coupled to an AFM Zeeman field, GdBiPt with A-type AFM spin order presents a metallic surface state on the terminations with AFM aligned Gd ions, and this surface state is independent of the strength of the AFM Zeeman field, i.e., this surface state will be preserved in a nonmagnetic case. Upon terminating the ferromagnetic spin-aligned Gd ions, the surface state is dependent on the strength of the Zeeman field, and the metallic surface can recover when the Zeeman field approaches zero.