Superconductivity Below 2.5K in Nb0.25Bi2Se3 Topological Insulator Single Crystal

Abstract

We report crystal growth and below 2.5K superconductivity of Nb0.25Bi2Se3. These crystals are grown by self-flux method. The X-ray diffraction (XRD) pattern of a grown crystal flake shows (00l) plane (c-orientation) growth. The Rietveld refinement of crushed crystal powder XRD (PXRD) pattern confirms the phase purity of the studied sample having R-3m space group of rhombohedral crystalline structure. The Raman spectrum of the studied Nb0.25Bi2Se3 crystal distinctly shows three well-defined vibrational modes in terms of A11g, Eg2, and A21g at around 72, 129, and 173 cm−1, which are slightly shifted in comparison with pure Bi2Se3. Magnetization studies in terms of field cooled (FC) and zero field cooled (ZFC) magnetic susceptibility measurements show the diamagnetic transition (Tconset) of the compound at around 2.5K and near saturation of the same below around 2.1K. The isothermal magnetization (MH) being taken at 2K revealed the lower critical field (Hc1) of around 50 Oe and the upper critical field (Hc2) of 900 Oe. It is clear that the studied Nb0.25Bi2Se3 is a bulk superconductor. The superconducting critical parameters thus calculated, viz the coherence length, upper and lower critical fields, and superconducting transition temperature for a grown Nb0.25Bi2Se3 single crystal are reported here.