ARPES Studies on the Origin of the High T_c in Quadruple-Layered Cuprate (Cu,C)Ba₂Ca₃Cu₄O_11+δ

In the same class of cuprate superconductors, the highest superconducting transition temperature (T_c) is consistently observed in system with three or four CuO₂ planes per structural unit (n=3 or 4). The mechanisms behind the elevated T_c​ in these multilayered cuprates remain debated. It was proposed that the high superconducting critical temperature (T_c) results from a combination of strong pairing strength provided by the inner CuO₂ planes (IPs) and large superconducting phase coherence from the outer CuO₂ planes (OPs), known as the "composite picture." However, definitive experimental evidence for this model remains elusive, particularly regarding whether T_c is suppressed if one of these planes ceases to be superconducting. Here, using high resolution ARPES, we performed systematic studies on quadruple-Layered cuprate (Cu,C)Ba₂Ca₃Cu₄O_11+δ with a high T_c=110K, and resolved the electronic structure of the IP and OP and their superconducting gaps as a function of temperature and momentum. We found that the OPs are not superconducting at the T_c of (Cu,C)Ba₂Ca₃Cu₄O_11+δ, while IP contribute to the pairing strength and phase stiffness concurrently to the system. Our findings offer new insights into understanding the origin of high T_c in multilayered cuprates.