Paramagnetism, hopping conduction, and weak localization in highly disordered pure and Dy-doped Bi2Se3nanoplates

Abstract

Breaking the topological protection of surface states of topological insulators is an essential prerequisite for exploring their applications. This is achievable by magnetic doping, in reduced dimensions, and predictably by introducing disorder beyond a critical level. In certain cases, the former is also known to induce a transition from weak anti-localization (WAL) to weak localization (WL). Here, we report the occurrence of paramagnetism, hopping conduction, and WL in chemically prepared unannealed Dy xBi 2 - xSe 3 (x = 0, 0.1, and 0.3) nanoplates primarily via dc magnetization, resistivity, and magnetoconductance measurements. The paramagnetism in the magnetic-atom-free Bi 2Se 3 nanoplates is ascribed, using density functional theory calculations, to the acquisition of magnetic moments by defects. The defect density in pure Bi 2Se 3 is estimated to be high (∼ 10 19 defects/cm 3). Successive Dy doping brings in further incremental disorder, apart from the Dy atomic moments. The nanoplates are shown to sequentially exhibit thermally activated band conduction, nearest neighbor hopping, Mott variable range hopping (VRH), and Efros-Shklovskii VRH with decreasing temperature. WL is evident from the observed positive magnetoconductance. Annealing converts the WL behavior to WAL, arguably by setting in the topological protection on a substantial reduction of the disorder.