Electronic Structure and Superconductivity in La_1.55Sr_0.45CuO₄/La₂CuO₄ Artificial High-T_c Superlattices Probed with Hard X-ray Photoelectron Spectroscopy

Recent advances in artificial high-temperature superconducting superlattices demonstrate how nanoscale design can be used to tune superconducting properties. We present spectroscopic evidence for the emergence of a superconducting dome associated with changes in the electronic structure near a Lifshitz transition in La_1.55Sr_0.45CuO₄/La₂CuO₄ superlattices. Using hard X-ray photoelectron spectroscopy (HAXPES), we probe both bulk and interfacial regions and observe temperature-dependent modification of the Fermi surface in optimally doped superconducting samples, together with effective-doping-dependent shifts in lanthanum, oxygen, and copper core levels. The evolution of the chemical potential extracted from lanthanum spectra indicates gradual modifications of the band structure across the transition region. These results provide direct spectroscopic insight into how electronic reconstruction at the nanoscale governs superconductivity in engineered oxide superlattices.