Structure-Property relationships and superconductivity in Single Crystals of Nb_xBi₂Ch₃, (Ch ≡ S, Se, Te)

Studies of Topological Insulators, possibly a new quantum phase of matter believed to possess a 2-dimensional Fermi surface, have led to a search for other insulators or semi-metals in which topologically non-trivial properties can be tuned using a chemical, structural, or external thermodynamic parameter. Topological insulators such as Bi₂Se₃ and Bi₂Te₃ have attracted much interest due to not just their non-trivial topology, but also due to the appearance of superconductivity upon intercalation or substitution with elements such as Cu, Sr and Nb. Many potentially interesting transition-metal intercalated/doped Bismuth-Chalcogenides have not yet been explored. Here, we discuss our growth and study of Nb_0.2Bi₂Ch₃ crystals (Ch ≡ S, Se, Te). We report resistivity measurements and confirm a superconducting transition near 3K for Nb_0.2Bi₂Se₃. We also report a possible charge density wave (CDW) transition in Nb_0.2Bi₂Te₃. In contrast, Nb_0.2Bi₂S₃ was found to be a good conductor with no phase transitions. Detailed fitting of x-ray diffraction shows that all three families of single crystals have a primary phase of Bi₂Ch₃ and a minor secondary phase of BiNbCh₃. We discuss our results together with Raman Spectroscopy, X-ray Diffraction and Electron Diffraction studies of our crystals.