Einladung Zum Physikalischen Kolloquium Photoelectron Momentum Microscopy -mapping of the Electronic Bandstructure within Minutes

Photoelectron Momentum Microscopy Mapping of the Electronic Bandstructure Within Minutes The electronic band structure of solids is readily described in reciprocal space (k-space). Owing to the translational symmetry of crystalline solids, the electronic structure can be reduced to the first Brillouin zone, which contains the full information on all electronic bands. Experimental band mapping via angleresolved photoelectron spectroscopy (ARPES) is characterized by excellent resolution (few meV/0.1°). ARPES has gained tremendous importance for the analysis of complex k-space topologies and 3D spin textures [1]. Energy analyzers allow parallel detection of certain angular and energy intervals; the band structure is reconstructed from sequential scans in different azimuthal planes. With increasing energy/angular resolution measurement speed has become an issue, especially for reactive surfaces and – dramatically– when it comes to spinresolved detection. Here a novel development towards simultaneous observation of the full k-distribution is presented. Based on concepts of electron microscopy it exploits the special imaging properties of “cathode-lens” type microscopes. Owing to kII-conservation in the photoemission process the reciprocal image formed in the backfocal plane of the cathode lens directly yields the (surface projected) bandstructure inside the crystal in the whole surface Brillouin zone. This novel momentum microscopy bears the potential of high momentum resolution, being mandatory in today’s materials research. Imaging dispersive analyzers allow acquisition of the kII-distribution at the selected energy in a very large momentum range [2]. Implementation of an imaging spin filter yields unprecedented spin-resolved acquisition speed with 2800 data points in parallel [3]. Going further in parallelization, we developed a true 3D-method for k-space mapping with utmost efficiency by implementing an imaging time-of-flight ToF spectrometer [4]. Fig. 1a illustrates the principle: All counting events in the E-kII paraboloid confined by the Fermi surface and the photoemission horizon (condition k⊥=0) are accumulated, typically >10 voxels simultaneously.