Investigate the Nb doping position and its relationship with bulk topological superconductivity in NbxBi2Se3 by X-ray photoelectron spectra

The relationship between the doping position of Nb in Bi2Se3 and its superconductivity is investigated by XPS, magnetic measurement and transport measurement. It is found that for NbxBi2Se3, the main impurity phase comes from BiNbSe3. Superconducting volume fraction of Nb doped Bi2Se3 increases with the ratio of Nb inserted in the van der Waals layers. The van der Waals-layer-position doped Nb may lead to superconductivity in Bi2Se3. This work may stimulate further investigation on topological superconductivity mechanism of NbxBi2Se3.