Survival of Topological Surface States in Cobalt Doped Sb2Te3

Sb2-xCoxTe3 (x = 0, 0.05, 0.3) nanostructures have been synthesized using microwave-assisted solvothermal synthesis technique. The x = 0 and x = 0.05 samples show a semiconducting-like resistivity with an upturn in the low temperature (T < 20 K) region and a gradual drop at the high temperature region. A metal-like resistivity at high temperature along with an upturn at low temperature is observed as the concentration of cobalt is increased to x = 0.3. Resistivity upturn of the samples is evaluated as the competition between electron-electron interaction (EEI) effect and quantum interference effect (QIE). Magnetoresistance (MR) of the x = 0 and x = 0.05 samples at the very low magnetic field and at low temperatures show disorder-induced weak localization (WL) which disappears at high temperature, whereas x = 0.3 sample shows only weak anti-localization (WAL). The high-field MR of x = 0 and 0.3 samples exhibits power law dependency at 2 K. High-field MR reveals the existence of the surface state as well as bulk state conduction in the materials. Thermoelectric power measurement of the nanostructures exhibits positive Seebeck coefficients denoting p-type carriers which vary quasi linearly with temperature and decrease with the incorporation of cobalt in the systems. An enhancement in power factor of 47% is observed near room temperature when the concentration of cobalt is increased from x = 0 to x = 0.3.