High- Tc Superconductivity: New Issues from Photoemission Data

Recent high-resolution photoemission results on high-Tc superconductors and other low-dimensional systems solve some critical issues but also open new fundamental questions. A recent breakthrough enabled us to clarify the interplay of conflicting periodicities in photoemission data, thus legitimizing the photoemission analysis of crystals with super-periodicities. On the other hand, results on the role of doping and of intentional disorder in Bi2Sr2CaCu2O8+x single crystals raise questions about the origin of the pseudogap.