Excess Carrier Density and the Role of Spin Density Waves in the Mechanism of High Tc Superconductivity in (Cu_0.5Tl_0.5)Ba₂Ca₂Cu_3-xK_xO_10-δ (x = 0, 1, 2, 2.5, 3) Samples

Samples (Cu_0.5Tl_0.5)Ba₂Ca₂Cu_3-xK_xO_10-δ (x = 0, 1, 2, 2.5, 3) and Tl_1.0Ba₂Ca₂K₃O_10-δ were synthesized to study the effect of electron donor atoms at the copper planar sites CuO₂ to better understand process of superconductivity in oxides. The samples were synthesized following the two-step solid-state reaction method, and analyzed using x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray fluorescence spectroscopy (XRF), resistivity (RT), and Fourier-transform infrared (FTIR) absorption measurements. By using the software VESTA (visualization for electronic and structural analysis), we have successfully drawn the crystal structures of all the samples. From room temperature to the onset of superconductivity, our samples showed metallic variation in resistivity, with zero resistivity at the critical temperature (Tc, R = 0) staying around 93 K. In the Tl_1.0Ba₂Ca₂K₃O_10-δ samples, copper Cu (3d⁹) atoms were entirely removed from the charge reservoir layer (i.e., Tl_1.0Ba₂O_4-δ charge reservoir layer) the samples showed semiconducting behavior with variable range Mott hopping (VRH) conductivity with an energy gap of 2.41 meV. The FTIR absorption spectrum demonstrated the planar oxygen mode, as well as the apical oxygen modes. Tl-O_A-Cu(2) and Cu(1)-O_A-Cu(2) were stiffened with the doping of K(4s¹) at the CuO₂ planar sites, confirming intrinsic doping of K atoms. Excess conductivity studies (FIC) of the Cu_0.5Tl_0.5Ba₂Ca₂Cu_3-xK_xO_10-δ (x = 1, 2, 2.5, 3) samples revealed an increase in the coherence length along the c-axis ξ_c(0), the Fermi velocity of superconducting carriers V_F, inter-layer coupling J, and the energy needed to break apart the Cooper pairs when compared with the un-doped Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10-δ, sample. Doped alkali atoms provide a larger density of free carriers in the superconducting planes rising superconductivity parameters. Higher free carrier density provided by the doped alkali atoms at room temperature to the conducting planes enhanced the electron–hole recombination process which brings them to the optimal doping level, thereby promoting the critical temperature and superconducting parameters to superior values. The Turning of the Tl₁Ba₂Ca₂K₃O_10-δ samples semiconducting has shown that the presence of a spin-bearing entity in the unit cell is important for the occurrence of high Tc superconductivity, and the interplay of spin and charge density waves induces superconductivity in oxide samples at high temperatures.