The transport of electrons is governed by the shape of the Fermi surface. We found that the topology of the Fermi surface of a semimetal can be manipulated on ultrafast timescales through optical excitation. A change in the Fermi surface topology, also called Lifshitz transition, can lead to the emergence of fascinating phenomena like colossal magnetoresistance and superconductivity. Combining time-resolved multidimensional photoemission spectroscopy and TDDFT+U simulations, we introduce a scheme for driving an ultrafast Lifshitz [more...]

The research group of Julia Stähler (Fritz Haber Institute and Humboldt-Universität zu Berlin) has found out that semiconductors can be converted to metals and back more easily and more quickly than previously thought. This discovery may increase the processing speed and simplify the design of many common technological devices.
Band bending at semiconductor surfaces induced by chemical doping or electric fields can create metallic surfaces with properties not found in the bulk, such as high electron mobility, magnetism or superconductivity. Optical generation of such metallic surfaces on ultrafast timescales would be appealing for high-speed electronics. It was demonstrated that the ultrafast generation of a metal at the (10-10) surface [more...]