Superconductivity below 2.5K in Nb0.25Bi2Se3 topological insulator single crystal

TL;DR

This study reports the synthesis and characterization of Nb0.25Bi2Se3 single crystals that exhibit superconductivity below 2.5K, with detailed analysis of their structural, vibrational, and magnetic properties confirming bulk superconductivity.

Contribution

First demonstration of superconductivity in Nb0.25Bi2Se3 single crystals with comprehensive structural and magnetic characterization.

Findings

Superconductivity observed below 2.5K in Nb0.25Bi2Se3

Critical magnetic fields Hc1 ≈ 50 Oe and Hc2 ≈ 900 Oe determined

Crystals confirmed to be phase pure with rhombohedral structure

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 as 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, A21g at around 72, 129 and 173cm-1, which are slightly shifted in comparison to 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 isothernal magnetization (MH) being taken at 2K, revealed the lower critical field (Hc1) of around 50Oe and the upper critical field (Hc2) of 900Oe. It is clear 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 as grown Nb0.25Bi2Se3 single crystal are reported here.