Theoretical and experimental investigations on Mn doped Bi2Se3 topological insulator

Magnetic ion doping in topological insulators (TI's) has emerged to be important both from technological point of view and for experimental verification of exotic fundamental physical concepts. Magnetic ion doping not only opens up the energy gap in surface states of a TI but also changes its bulk band structure significantly. To observe the effect of magnetic ion doping on electronic band structure of TIs density functional theory based ab initio electronic structure calculations have been carried out on 2%, 4% and 6% Mn doped ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ system. To validate the results single crystal of undoped and Mn doped ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ have been grown and have been characterized by angle-resolved photoemission spectroscopy (ARPES) measurements with synchrotron radiation. Most of the results viz., band inversion, gapless surface states and reduction in band gap due to Mn doping, as obtained by theoretical calculations have been verified by ARPES measurements. Additionally, ARPES measurements show opening up of the gapless surface states in Mn doped samples. The samples have also been subjected to x-ray absorption spectroscopy measurements comprising of x-ray near edge structure and extended x-ray absorption fine structure measurements using synchrotron radiation which together conclusively show that Mn ions substitute at Bi sites in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ lattice.