Cu1234 single crystals growth with contamination-free quality

The CuBa₂Ca₃Cu₄O_10+δ (Cu1234) superconductor exhibits a unique combination of high critical temperature (118 K ambient T_c), high critical current density (J_c), and high irreversibility field (H_irr), i.e., the so-called triple-high attributes, making it a promising candidate for high-temperature and high-field applications. However, the growth of high-quality single crystals has been hindered by contamination from traditional sample capsules used in conventional high-pressure synthesis, leading to suppressed T_c. In this work, we develop a modified high-pressure sample assembly utilizing a capsule with MgO as the inner layer and Pt as the outer layer, which effectively prevents undesirable doping of Pt into Cu1234 that suppresses T_c. This approach enables the successful growth of Cu1234 single crystals with a sharp superconducting transition at T_c ∼ 115 K, comparable to that of polycrystalline samples. Structural and compositional analyses confirm the phase purity, strong c-axis orientation, and near-ideal stoichiometry close to the Cu1234 formula. These high-quality Cu1234 single crystals provide a reliable platform for elucidating the intrinsic mechanisms of the exceptional triple-high superconducting properties of the Cu1234 system.