Abstract
We perform ab-initio calculations on Bi$_\mathrm{{Se}}$ antisite defects in the surface of Bi$_2$Se$_3$, finding strong low-energy defect resonances with a spontaneous ferromagnetism, fixed to an out-of-plane orientation due to an exceptional large magnetic anisotropy energy. For antisite defects in the surface layer, we find semi-itinerant ferromagnetism and strong hybridization with the Dirac surface state, generating a finite energy gap. For deeper lying defects, such hybridization is largely absent, the magnetic moments becomes more localized, and no energy gap is present.
Highlights
We perform ab initio calculations on BiSe antisite defects in the surface of Bi2Se3, finding strong lowenergy defect resonances with a spontaneous ferromagnetism, fixed to an out-of-plane orientation due to an exceptionally large magnetic anisotropy energy
We show how the net magnetization varies as a function of defect concentration for the BiSe1 and BiSe2 defects. We find that both spin and orbital moments increase with decreasing concentration: The surface BiSe1 defect shows an almost threefold increase in the spin magnetic moment when decreasing the defect concentration from 25% to 6%, while the subsurface BiSe2 defect shows a minor increase
Our fully relativistic ab initio calculations show that intrinsic antisite BiSe defects in the surface layer of the Topological insulators (TIs) Bi2Se3 generate a finite energy gap in the topologically protected Dirac surface state (DSS)
Summary
Suhas Nahas ,* Biplab Sanyal,† and Annica M. The DSS spectrum is gapped due to TRS breaking, but at the same time the nonmagnetic part of the scattering potential produces localized impurity-induced resonances [44,45,46,47,48] filling up the gap [49] In this Rapid Communication, we show that a surface energy gap is generated in the most common TI, Bi2Se3, from intrinsic BiSe antisite defects, entirely without the need for foreign magnetic atoms.
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