Electronic and transport properties of the Mn-doped topological insulatorBi2Te3: A first-principles study

We present a first-principles study of the electronic, magnetic, and transport properties of the topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ doped with Mn atoms in substitutional $({\mathrm{Mn}}_{\mathrm{Bi}})$ and interstitial van der Waals gap positions $({\mathrm{Mn}}_{i})$, which act as acceptors and donors, respectively. The effect of native ${\mathrm{Bi}}_{\mathrm{Te}}$- and ${\mathrm{Te}}_{\mathrm{Bi}}$-antisite defects and their influence on calculated electronic transport properties is also investigated. We have studied four models representing typical cases, namely, (i) ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ with and without native defects, (ii) ${\mathrm{Mn}}_{\mathrm{Bi}}$ defects with and without native defects, (iii) the same, but for ${\mathrm{Mn}}_{i}$ defects, and (iv) the combined presence of ${\mathrm{Mn}}_{\mathrm{Bi}}$ and ${\mathrm{Mn}}_{i}$. It has been found that lattice relaxations around ${\mathrm{Mn}}_{\mathrm{Bi}}$ defects play an important role for both magnetic and transport properties. The resistivity is strongly influenced by the amount of carriers, their type, and by the relative positions of the Mn-impurity energy levels and the Fermi energy. Our results suggest strategies to tune bulk resistivities and also clarify the location of Mn atoms in samples. Calculations indicate that at least two of the considered defects have to be present simultaneously in order to explain the experimental observations, and the role of interstitials may be more important than expected.