Study of phonon modes and superconducting properties of the oxygen post-annealed (Cu_(0.5)Tl_(0.5))Ba_2Ca_(n-1)(Cu_(n-y)Ge_y)O_(2n+4-delta) (n = 3, 4 and y = 0, 0.5, 0.75, 1.0) superconductors

摘要

Superconducting properties of the Ge doped (Cu_(0.5)Tl_(0.5))Ba_2Ca_(n-1)(Cu_(n-y)Ge_y)O_(2n+4-delta) (n = 3,4 andy = 0, 0.5, 0.75, 1.0) superconductors have been enhanced by carrying out annealing in the flowing oxygen atmosphere. With Ge doping superconducting properties were suppressed but after the oxygen annealing substantial enhancement has been observed in both critical temperature and magnetic susceptibility in all the samples. The enhanced superconductivity in the post-annealed samples is most likely caused by the optimization of the carrier density in the conducting CuO_2/GeO_2 planes. Oxygen related various phonon modes of these samples have also been investigated and possible role of Ge in modifying these modes has been discussed. Since properties of Ge are very well known, therefore, its doping can be useful for understanding of mechanism of superconductivity.