Microscopic characterization of the superconducting thin films of the (Cu_1-xC_x)Ba₂Ca_n-1Cu_nO_y on LaAlO₃ substrate

Abstract The cuprate superconductors with transition temperature over 100 K are mainly Hg-based, Tl-based, Bi-based and Cu-based. The transition temperature of the Cu-based superconductor (Cu 1-x C x )Ba 2 Ca 3 Cu 4 O y reaches up to 117 K, while exhibiting the highest irreversibility field (15 T @ 86 K), without toxic elements, and with low anisotropy. This greatly enhances its applicability in strong magnetic fields, making it highly competitive. However, the growth of (Cu 1-x C x )Ba 2 Ca 3 Cu 4 O y bulk materials requires high temperature and high pressure, which greatly limits the practical application of (Cu 1-x C x )Ba 2 Ca 3 Cu 4 O y . It was found that thin films of (Cu 1-x C x )Ba 2 Ca 3 Cu 4 O y can be grown using pulsed laser deposition and molecular beam epitaxy without the need of high pressure. In this paper, a -axis (Cu 1-x C x )Ba 2 Ca 3 Cu 4 O y thin films were successfully grown on LaAlO 3 single crystal substrate by pulsed laser deposition. However, the films exhibit a relatively low transition temperature of approximately 60 K. Herein, to ascertain the film’s microscopic structure, transmission electron microscopy illustrates that the film also contains additional minor superconducting phases such as (Cu 1-x C x )Ba 2 Ca 1 Cu 2 O y , (Cu 1-x C x )Ba 2 Ca 2 Cu 3 O y , and (Cu 1-x C x )Ba 2 Ca 4 Cu 5 O y in addition to the desired phase (Cu 1-x C x )Ba 2 Ca 3 Cu 4 O y . Furthermore, due to the epitaxial growth of the film with a significant lattice mismatch, it experiences tensile strain. (Cu 1-x C x )Ba 2 Ca 3 Cu 4 O y is easily to intergrow of phases with different n to minimize strain. The combination of these two factors contributes to the relatively low superconducting transition temperature in the film. In addition, a greater degree of disorder would reduce the superconducting transition temperature further.