Structural and electronic properties of manganese-doped Bi₂Te₃epitaxial layers

Abstract

We show that in manganese-doped topological insulator bismuth telluride layers, Mn atoms are incorporated predominantly as interstitials in the van der Waals gaps between the quintuple layers and not substitutionally on Bi sites within the quintuple layers. The structural properties of epitaxial layers with Mn concentration of up to 13% are studied by high-resolution x-ray diffraction, evidencing a shrinking of both the in-plane and out-of plane lattice parameters with increasing Mn content. Ferromagnetism sets in for Mn contents around 3% and the Curie temperatures rises up to 15 K for a Mn concentration of 9%. The easy magnetization axis is along the c-axis perpendicular to the (0001) epilayer plane. Angle-resolved photoemission spectroscopy reveals that the Fermi level is situated in the conduction band and no evidence for a gap opening at the topological surface state with the Dirac cone dispersion is found within the experimental resolution at temperatures close to the Curie temperature. From the detailed analysis of the extended x-ray absorption fine-structure experiments (EXAFS) performed at the MnK-edge, we demonstrate that the Mn atoms occupy interstitial positions within the van der Waals gap and are surrounded octahedrally by Te atoms of the adjacent quintuple layers.New J. Phys. 17 (2015) 013028 J Růžička et al

Applications of a L1‐Regularized Linear Regression to X‐Ray Fluorescence Holography Data of Functional Materials

“…Thus, small shrinks of the lattice are caused by the neighboring Te atoms. This result is compatible with the XRD data measured by Růžička et al…”

“…By adding transition metals, it changes to show a TI behavior. The existence of the Dirac cone in the surface state electronic density of states was confirmed in Mn‐doped Bi 2 Te 3 by an angle‐solved photoemission spectroscopy investigation …”

Experimental and density functional study of Mn doped Bi2Te3 topological insulator

“…11 The main goal of achieving room-temperature ferromagnetism in homogeneously doped 3D TIs has therefore proven difficult to achieve. 14 Although Mn doped Bi 2 Te 3 crystals and thin films with doping concentrations of up to 10% were found to be ferromagnetic with Curie temperatures of around 10 K, 15 it is not clear if ferromagnetism is due to secondary, undesirable Mn-containing phases or the homogeneous doping of Mn into the Bi 2 Te 3 matrix, i.e., as a substitutional dopant. Due to the layered crystal structure of these materials, several possible lattice sites exist for the incorporation of magnetic dopants.…”

“…These include substitutional incorporation on Bi or Te sites within the QLs, as well as interstitial incorporation within the QLs, and the incorporation in the van der Waals gap between the QLs. 15 In these ternary systems, it is of great importance to preserve the overall bulk electronic properties upon doping, and, moreover, to reduce the defect densities in general.…”

High-resolution x-ray diffraction of epitaxial bismuth chalcogenide topological insulator layers

“…However, little is known about the real structure and crystal quality of Bi m X n thin films grown by molecular beam epitaxy (MBE). In our previous papers [14][15][16] we investigated the crystal structure of MBE grown epitaxial Bi 2 Te 3 and Mn-doped Bi 2 Te 3 layers using highresolution x-ray diffraction (HRXRD) and x-ray absorption spectroscopy (EXAFS) and angle-resolved photoelectron spectroscopy (ARPES). We found that the chemical composition, crystal structure as well as the crystal quality substantially depend on the excess flux of Te during the MBE growth.…”