Center for Functional Nanomaterials Seminar

The deep understanding of High-Tc superconductors has been one of the biggest challenges of solid state physics for more than two decades. After 20 years of investigation, a full knowledge of the underlying pairing mechanism has not been achieved. High-Tc superconductors belong to a wider group of complex materials (highly correlated materials) which includes Mott insulators and charge density wave materials, among others. The behavior of these systems is governed by many-body interactions, as electronic correlations or electronic coupling with other excitations, like atomic vibrations (phonons) or spin fluctuations. The complexity of these materials requires the use of powerful experimental techniques for their study, and further knowledge can be gained from the use of several techniques in a complementary way. In this talk I will illustrate this approach with two main examples. In the first one, the 1/3ML-Sn/Ge(111) interface, a two-dimensional model system with a triangular lattice, will be considered. The study of this interface by Angle Revolved Photoemission Spectroscopy (ARPES), complemented with Scanning Tunneling Microscopy (STM) and Low Energy Electron Diffraction (LEED), has allowed us to observe the formation of a Mott insulating phase below 30 K. In the second example, the study of three compounds of the family of the new class of Iron-based high-Tc superconductors, by time- and Angle-Revolved Photoemission Spectroscopy (trARPES), will be presented. In addition, other examples where the application of the above mentioned techniques has proven to be useful for the understanding of complex materials will be also mentioned.