Topological insulators represent a novel state of matter where the surface charge carriers have a massless Dirac dispersion and are protected from backscattering by time reversal symmetry. So far, the materials used are exclusively based on band semiconductors. Only very recently it was realized that also strongly correlated materials can also be topological non trivial, with even the added possibility to find also phenomena more exotic than the ones in the topological band semiconductors. From a practical point of view, one may also expect that strong correlations will reduce the disturbing effect of impurities and at the same time increase the Fermi velocities of the topological surface states.
Our objective is now to investigate the electronic structure of selected rare-earth Kondo insulators to determine whether or not they can have topological non-trivial properties. Here we make use of very recent theoretical developments [Dzero-Sun-Galitski-Coleman, Phys. Rev. Lett., 104, 106408 (2010)] which predict that the presence of the strong spin-orbit coupling of the rare earth 4f shell and the level inversion of the rare-earth 4f and the 4d/5d bands can indeed produce non-trivial topology, provided that the orbital symmetry of the occupied 4f level fulfills certain conditions. The experimental work will make use of a variety of modern synchrotron based spectroscopies, including x-ray absorption spectroscopy, inelastic x-ray scattering (in collaboration with Dr. A. Severing) and angle-resolved photoemission.