Colloquium: Dr. G. D. VarmaDr. G. D. Varma Department of Physics Indian Institute of Technology Roorkee Roorkee-247667, India
Synthesis and Study of Superconducting Properties of MgB2 and Fe-Chalcogenide Superconductors
Super conductivity has been a fascinating area of research in the condensed matter physics since its discovery in 1911. During the last ~30 years many new classes of superconductors have been discovered which have created lot of excitement in both experimentalists and theoreticians working in the area of condensed matter physics. Among the various classes of superconductors, MgB 2 and Fe-based superconductors are more attractive due to their simple chemical compositions and application potential. Since the discovery of superconductivity at 39 K ( T c ) in MgB 2, lot of efforts are being made to improve its superconducting properties. In addition to high T C , large values of infield critical current density ( Jc(H) ), upper critical magnetic field ( H C2 ) and irreversibility field ( H irr ) are required for applications of a superconducting material for high field magnets. Unlike cuprate high temperature superconductors, the absence of weak links at grain boundaries in MgB 2 makes it a potential candidate for technological applications. Many efforts have been made to improve the superconducting properties of MgB 2 . Among them, chemical doping has been found most effective method to improve the superconducting properties ( J C , H C2 , H irr ) of MgB 2 . We have studied the effect of addition of various compounds on the superconducting properties of MgB 2 . Furthermore, the recent discovery of nonconventional superconductivity in Fe-based compounds has created a lot of interest among the condensed matter physicists and material scientists working in both theoretical and experimental areas. Among the family of Fe-based superconductors, the Fe-based chalcogenides are more interesting materials. These materials show large enhancement in T C with application of pressure. Furthermore, intercalations of alkali metals and a spacer layer between FeSe layers increase T C above ~30 K. We have grown single crystalline, polycrystalline and thin film samples with compositions FeTe 1-x Se x (0≤x≤0.6) to study structural, magnetic and superconducting properties of the grown samples. The variation in superconducting properties ( T C , H C2 and H irr ) with compositions of (Se,Te) has been studied. X-ray diffraction technique has been employed for structural characterization of the synthesised samples. Magnetic and magneto-transport measurements have been performed to study the magnetic and superconducting properties of the samples. In this talk the results of the work related to study of structural, magnetic and superconducting properties of MgB 2 and Fe-chalcogenide superconductors being carried out in our group will be described and discussed.