Enhanced three-dimensional excess conductivity in Be-doped Cu0.5Tl0.5Ba2Ca3−xBex Cu4O12−δ (x=,0.5,0.75,1.0,1.25,1.5) superconductors

Abstract

We report the enhanced fluctuation-induced conductivity of Be-doped Cu0.5Tl0.5Ba2Ca3−xBex Cu4O12−δ (x=0,0.5,0.75,1.0,1.25,1.5) samples. The analysis has been done with partial substitution of Be in place of Ca. In each case excess conductivity has been analyzed and we tried to make a fit with the Aslamasov–Larkin (AL) and Lawrence–Doniach equations. It is observed that our data fit well with the three-dimensional (3D) AL equation, and a crossover from two dimensions to three dimensions has been found in our samples. We have also employed this transition to estimate the Josephson coupling strength in our samples. This interlayer coupling strength J, which controls the superconducting transition, has been found to improve with increased Be content. The Ginzburg–Landau coherence lengths ξc(0) for all cases have also been calculated. The Fourier transform infrared spectroscopy (FTIR) absorption measurements also provide a clue for the enhanced 3D fluctuations. The higher electronegativity, as well as smaller ionic size, of Be compared to Ca is suggested to be the possible source of promoting enhanced 3D character in Be-doped samples.

Suppression of Superconductivity by Anharmonic Oscillations in Zn- or Ni-doped Cu0.5Tl0.5Ba2(CaMg)Cu1.5M1.5O10-δ (M=Zn, Ni) Superconductors; Evident by Magnetic Measurements

“…1 The optimal doped conducting CuO 2 planes impart a higher critical temperature T c to these compounds, showing the importance of carrier density in the mechanism of superconductivity. [2][3][4][5][6][7] The question is whether there is any role (3d 9 state imparts a small spin to Cu atoms in the CuO 2 plane) of remnant spin in the mechanism. To investigate any possible spin occurrence of Cu atoms in the conducting plane, we doped spin-less Zn 2+ (3d 10 ) atoms at the Cu site in the CuO 2 planes of Cu 0.5 Tl 0.5 Ba 2 Ca 2 (Cu 3-y Zn y )O 10-δ and Cu 0.5 Tl 0.5 Ba 2 Ca 3 (Cu 4-y Zn y )O 12-δ superconductors.…”

“…We concluded from those studies the existence of electron-phonon interactions in the mechanism of high T c superconductors. 4,15,16 To further elaborate the importance of electron-phonon interactions in such compounds, we doped Mg at the Ca sites; Mg has a smaller ionic radius and higher electronegativity in comparison with Ca atoms. [17][18][19] The size of Mg is smaller than Ca and the doped species is expected to decrease the distance between the CuO 2 planes, which in turn would further enhance the magnitude of anharmonic oscillations that would suppress the superconductivity.…”