Superconductivity and Localization in Disordered Superconductors

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Addis Ababa University


The effect of disorder due to nomagnetic impurities on superconductivity of Bi2Sr2CaCu2O8+x was investegated theoretically employing the matrix Green function in Nambu formalism. The relationship between disorder parameter and superconducting critical temperature has been calculated analytically for each of its possible pairing symmetries. The obtained results indicate that diluted nonmagnetic disorder has no significant e_ect on superconducting critical temperature of the system when the pairing symmetry is s-wave. On the other hand, the results obtained for the d-wave pairing symmetries show that disorder can significantly suppress the superconducting critical temperature of the system. Moreover, the results reveal that the supression of Tc depends on the strength of the impurity potential, the concentration of scatterers and the anisotropy of the pairing symmetries. The e_ect of disorder due to randomness in island potential on superconductivity of thin films was also investigated theoretically based on the hard core boson model developed for superfluid helium. The relationship between superconducting order parameter and disorder paramters was found analytically using the double time retarded Green function formalism. The obtained results indicate that disorder induced due to randomness in island potential enhances decoherence of Cooper pairs and suppresses superconducting order parameter and superfluidity of the system. The results also indicate that increasing the two-body interaction strength suppresses superconductivity of the system. The critical values of disorder and interactin strength at which the system completely ceases its superconductivity was also determined. Below these critical values, the system acts as a superconductor, a system with zero electrical resistance. Above the critical values, it acts as an insulator, a system with infinite electrical resistance. Finally, the e_ect of pressure on superconductivity of Pb and MgB2 was investigated theoretically based on density functional theory as implemented in Quantum ESPRESSO



Superconductivity, Localization, Disordered Superconductors