Interface-Dominated Topological Transport in Nanograined Bi₂Te₃

Bismuth telluride is an excellent thermoelectric material and also belongs to the class of three-dimensional topological insulators. Therefore, surface charge carriers with extremely high mobility exist at the crystal surfaces. This is particularly visible in nanoparticulate samples, provided that the nanoparticles used have sufficient surface purity. Compacted nanoparticulate bulk samples exhibit a high density of interfaces. These samples show a pronounced weak anti-localization in the low-temperature transport behavior as well as a kink in the electrical resistance at about 5 K. Evaluation of the magnetotransport data using the Hikami-Larkin-Nagaoka model yields coherence lengths of up to 200 nm, which is significantly larger than the average grain size in the studied samples. Using terahertz spectroscopy, the average mobility of the surface charge carriers can be estimated to be about 1000 to 10000 cm²V^-1s^-1 at room temperature. This means that good thermoelectric properties of nanoparticulate Bi₂Te₃ near room temperature are also determined in part by the existence of surface charge carriers.