Design and Differentiation of Quantum States at Subnanometer Scale in La 2 CuO 4 - Sr 2 CuO 4-δ Superlattices.

We present a study on the properties of superlattices made of ultrathin Sr 2 CuO 4-δ layers sandwiched between La 2 CuO 4 layers beyond the antiferromagnetic insulating nature of the individual layers of choice. Using molecular beam epitaxy, we synthesized these superlattices and observed superconductivity and metallicity at the interfaces. We probed the hole distribution to determine the discernible quantum states and found that the high-quality epitaxy, combined with mapping the electronic fine structure by electron energy-loss spectroscopy, allowed for the differentiation of insulating, metallic, and superconducting layers at the atomic-column scale. Our results demonstrate the possibility of exploring specific electronic properties at the subnanometer scale and highlight the potential of utilizing metastable Sr 2 CuO 4-δ slabs.