Enhancing Superconductivity in Cu_1/2Tl_1/2Ba₂Ca₂Cu₃O_10−δ with Graphene Incorporation: A Comprehensive Study

We report a significant enhancement in superconducting properties of the Cu_1/2Tl_1/2Ba₂Ca₂Cu₃O_10-δ (CuTl-1223) superconductor through the incorporation of graphene. The graphene quantum dots (GQDs) added to G_<i>x</i>/CuTl-1223 superconductors were synthesized by the solid-state reaction method and characterized using various analytical techniques including X-ray diffraction, temperature-dependent resistivity measurements, scanning electron microscopy, Fourier-transform infrared (FTIR) spectroscopy, and excess conductivity analyses. We found that all synthesized samples exhibit orthorhombic crystal structure, with the <i>c</i>-axis length and unit cell volume increased with the incorporation of GQDs. Notably, the zero-resistivity critical temperature has increased with higher GQDs content. Analysis of FTIR absorption spectra revealed a noticeable hardening of the apical oxygen and planar phonon mode (Cu(1)-O_<i>A</i>-Cu(2), CuO₂) with increasing GQDs concentration in the final compound. The sample morphology reveals that carbon from the graphene has been successfully incorporated in the CuTl unit cell, acting as an efficient pinning center. Excess conductivity analyses provided insights into the effects of GQDs on the coherence length along the <i>c</i>-axis, interlayer coupling, and Fermi velocity of carriers within the CuTl-1223 unit cell, showing a decrease followed by enhancement with further addition of GQDs. Additionally, parameters such as B_<i>c</i>0(T), B_<i>c</i>1(T), and J_<i>c</i>0(0) exhibited an increase with the incorporation of GQDs, suggesting a rise in the superconductor's volume fraction in the final compound. Overall, these findings will contribute to a deeper understanding of the role of GQDs in enhancing the superconducting properties of G_<i>x</i>/Cu_1/2Tl_1/2Ba₂Ca₂Cu₃O_10-δ superconductors.