One of the specific subjects under investigation is the role/interplay of microscopic electronic inhomogeneity and site-specific chemical disorder in the high-temperature superconductors. Microscopic spatial variations of the carrier density and superconducting gap were recently observed on Bi2Sr2CaCu2O8+d (Bi2212) by mean of scanning tunneling microscopy experiments. These results attracted a lot of attention and were interpreted as evidence for local charge inhomogeneity, for which an intrinsic nature and a close connection to superconductivity were suggested [1]. Alternatively it was proposed that electronic inhomogeneities may also be triggered by site-specific chemical disorder [2], which was shown to have a dramatic effect on TC (as shown in Fig.1, the record value of TC=96 K was obtained for Bi2212 by controlling the amount and location of disorder).
In this regard we are investigating the electronic properties of Bi-cuprates in which off-stoichiometry and chemical disorders have been carefully tuned. These more chemically ordered samples are ideally suited to study the role of charge inhomogeneity by ARPES as well as STM, and also to address whether long range charged ordering is realized at very low doping levels, which can be investigated directly by resonant X-ray scattering experiments. By mean of these comprehensive and complementary studies we aim at conclusively addressing whether the nanoscale phase separation is of intrinsic nature in the cuprates and, in addition, what is the relevance of this phenomenon to high-Tc superconductivity.