The problem of superconductors has been a central issue in Solid State
Physics since 1987. After the discovery of superconductivity (HTSC) in
doped perovskites, it was realized that the HTSC appears in an unknown
complex electronic phase of c- densed matter. In the early years, all
theories of HTSC were focused on the physics of a homogeneous 2D metal
with large electron-electron correlations or on a 2D polaron gas. Only
after 1990, a novel paradigm started to grow where this 2D metallic
phase is described as an inhomogeneous metal. This was the outcome of
several experimental evidences of phase separation at low doping. Since
1992, a series of conferences on phase separation were organized to
allow scientists to get together to discuss the phase separation and
related issues. Following the discovery by the Rome group in 1992 that
"the charges move freely mainly in one direction like the water running
in the grooves in the corrugated iron foil," a new scenario to
understand superconductivity in the superconductors was open. Because
the charges move like rivers, the physics of these materials shifts
toward the physics of novel mesoscopic heterostructures and complex
electronic solids. Therefore, understanding the striped phases in the
perovskites not only provides an opportunity to understand the anomalous
metallic state of cuprate superconductors, but also suggests a way to
design new materials of technological importance. Indeed, the stripes
are becoming a field of general scientific interest.
