Single crystal growth of V-doped NbSe2 superconductor and physical properties measurements

Abstract

In this work we represent the effect of V atoms in the superconducting properties of NbSe2 single crystal. The V atom is successfully intercalated in the layered structure of NbSe2 and is stable at the low concentration of V atoms. The XRD pattern of V-NbSe2 single crystal shows the high purity of the samples along with the highly directional alignment of the planes along the c-axis. The Rietveld refinement of the XRD data of NbSe2 and V-NbSe2 superconductors have been done with FullProf software. The lattice parameters which were extracted after refinement show a decrease in lattice constants and volume of NbSe2 with the increasing V concentration, that confirms the intercalation of V atoms in the interlayer spacing of NbSe2. The critical temperature (Tc) of NbSe2 decreases with increasing the V concentration, which might be due to change of band structure and an extra influence due to the attractive electron coupling through an electron excitation interaction. The magnetization measurements have been used to determine the effect of V impurities on the different parameters such as upper critical field (Hc2), irreversible field (Hirr), coherence length, critical current density (Jc) and the pinning mechanism in NbSe2 single crystals. The upper critical field decreases with increasing V concentration in NbSe2. The Jc values were calculated using the Critical Bean Model. Upon increasing the concentration of V impurities, the superconducting critical current density (Jc) has been enhanced appreciably compared to the pure NbSe2. We obtained Jc (0) (2K) ~ 541084, 389668, 841546 Acm-2 respectively for V0.0007NbSe2, V0.001NbSe2, V0.0015NbSe2 samples and decreases with increasing temperature and magnetic field, indicating the presence of weak pinning phenomena occurring at the surrounding of the impurities which act as pinning point centers. The disorder created in NbSe2 single crystal due to V impurity shows δl flux pinning, stating that defects are small and point sized. A low value of hmax in the studied single crystals of V-NbSe2 suggests that pinning in V-NbSe2 superconductor is due to the presence of a large density defect centres. Furthermore, the field dependence behaviour of the pinning force density of V-incorporated NbSe2 represents the existence of both surface pinning and the xii point pinning effect. We figured the flux pinning force density and shown the existence of point core pinning of the normal centres in the low field regime. The present outcomes are significant in understanding of the layered NbSe2 superconductors and its applications.