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Interfaces of Novel Materials

Unoccupied Electronic States of Topological Insulators

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Recently, a class of materials with novel electronic properties at the surface has been predicted. The so called topological insulators show a unique electronic structure at the surface. The surface states of these materials show a linear dispersion and the spin degeneracy of the bands is lifted. In addition to that the number of fermilevel crossings at the Gamma point is always odd. The structure therefore resembles a Dirac-Cone. This band-structure is famous in graphene, but here we have the advantages of a small parallel momentum of the electrons.

Our group is investigating topological insulators with two-photon-photoemission, because this method allows us to directly investigate the dynamics and lifetimes of electrons inside the dirac cone. Using 2ppe, we were able to show that for the two materials Sb2Te3 and Sb2Te2Se there is indeed a linear dispersing surface state and that transport from the surface to the bulk seams to play a substantial role for the electron dynmics inside the dirac cone. More...


Surface and Interface States of Periodically Rippled Graphene/Ru(0001)

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There is fast-growing interest in understanding the interaction of graphene with metal substrates. By means of thermal decomposition of unsaturated hydrocarbon species on transition metal substrates, the fabrication of very large and extremely well-defined graphene sheets can be realized. Moreover, metal contacts are of high relevance to graphene-based electronic devices. In terms of the electronic structure, angle-resolved photoelectron spectroscopy has already provided information about the occupied states of graphene on different substrates. Comparatively little, however, is known about unoccupied states above the Fermi level and even less on dynamics of electron transfer processes between graphene layers and metals.

In our study we explored the unoccupied electronic states of epitaxially grown graphene on Ru(0001) by time-, energy- and angle-resolved two-photon photoemission. We identify a Ruthenium derived resonance and a graphene/Ruthenium interface state at 0.91 and 2.58 eV above the Fermi level, as well as three image-potential derived states close to the vacuum level. The most strongly bound, short-lived, and least dispersing imagepotential state is suggested to have some quantum-well character with a large amplitude below the graphene hills. The two other image-potential states are attributed to a series of slightly decoupled states. Their lifetimes and dispersions are indicative of electrons moving almost freely above the valley areas of the moiré superlattice of graphene. More...

Zuletzt aktualisiert: 27.05.2015 · armbrusn

 
 
 
Fb. 13 - Physik

Surface Physics, Renthof 5, D-35032 Marburg
Tel. +49 6421/28-24216, Fax +49 6421/28-24218, E-Mail: Irene.Dippel@physik.uni-marburg.de

URL dieser Seite: https://www.uni-marburg.de/fb13/researchgroups/of/dynamics/novel_materials_if.hmtl

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