Impurity position and lattice distortion in a Mn-doped Bi2Te3 topological insulator investigated by x-ray fluorescence holography and x-ray absorption fine structure

Abstract

Mn $K\ensuremath{\alpha}$ x-ray fluorescence holography (XFH) measurements were performed on a single crystal of a ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}{\mathrm{Mn}}_{0.1}$ topological insulator at 100 and 300 K to search for the impurity sites of the Mn atoms in this functional crystal. The three-dimensional atomic images were reconstructed using an ${L}_{1}$-regularized linear regression. X-ray absorption fine-structure (XAFS) experiments were also carried out at 30--300 K to obtain additional structural information. The local structural information was obtained from these data, such as the positions of the Mn impurity sites, the Mn-Te interatomic distances, the lattice distortions, and the positional fluctuations around the impurity Mn atoms. The possible Mn impurity sites are twofold, i.e., an interlayer site with an octahedral symmetry and a substitutional site of Te on the layer surface. A distinct temperature dependence is seen in the positional fluctuations of the impurity Mn atoms in the substitutional site. These findings for the impurity sites cannot be easily obtained by diffraction or XAFS experiment in the usual way, but only using a combination of the XFH and XAFS measurements.