Imaging the impact of single dopants on the competing phases of the high-Tc superconductor Bi2+ySr2-yCaCu2O8+x
High-Tc cuprate superconductors display startling nanoscale disorder in essential properties such as band structure, pseudogap energy scale, and even superconducting critical temperature. However, the underlying cause of this disorder remains mysterious; theoretical explanations have ranged from chemical inhomogeneity to spontaneous electronic phase separation. We extend the energy range of scanning tunneling spectroscopy, allowing the first-ever direct mapping of all three types of oxygen dopants in Bi2+ySr2-yCaCu2O8+x. We show that a subset of these dopants are indeed the direct cause of the nanoscale disorder. We investigate a range of underdoped samples and explain how the spatial variations in competing electronic orders, such as the pseudogap and the charge density wave, are governed by the disorder in the dopant concentrations, particularly vacancies in the apical oxygen site. We suggest a possible avenue to raise Tc in this material.