Thickness Dependence of High-Temperature (Cu,C)Ba2Ca3Cu4Oy Superconducting Films with Large Irreversible Field

(Cu,C)Ba₂Ca₃Cu₄O_y ((Cu,C)-1234) is a nontoxic, non-rare-earth-element-included superconducting material characterized by high critical temperature T_C, critical current density J_C, and irreversible field μ₀H_irr. The growth of superconducting (Cu,C)-1234 thin films by using the pulsed laser deposition (PLD) method circumvents the challenges associated with high-pressure bulk crystal growth. Nonetheless, several critical aspects regarding the growth mechanism, strain effects, and thickness-dependent behavior in PLD-grown (Cu,C)-1234 thin films remain poorly understood. Here, the thickness dependence of the superconducting properties in (Cu,C)-1234 thin films is reported systematically. Highly oriented, a-axis (Cu,C)-1234 films on LaAlO₃ (LAO) (1 0 0) substrates, with thickness ranging from 25 to 500 nm, is realized. Transport measurements reveal that films with a critical thickness of ∼250 nm exhibit optimized superconducting performance, as characterized by uniform surface morphology, high critical temperature, strong pining energy, and large irreversible field. Moreover, films near this optimal thickness display an increase in the irreversible field μ₀H_irr, approximately 9 T at 49 K (0.77T_C), which could be attributed to an elevated effective pinning barrier. This result paves the way for the application of the (Cu,C)-1234 thin film under high magnetic fields.