Berlin 2012 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 17: Poster Session

MM 17.87: Poster

Montag, 26. März 2012, 17:00–19:00, Poster B

A new 2D-ACAR spectrometer at the NEPOMUC positron facility — •Hubert Ceeh¹, Josef Weber¹, Christoph Hugenschmidt^1,2, Michael Leitner³, and Peter Böni¹ — ¹Technische Universität München E21, Garching, Germany — ²Forschungs-Neutronenquelle Heinz Maier-Leibnitz, Garching, Germany — ³Technische Universität München E13, Garching, Germany

The 2D-ACAR (Angular Correlation of Annihilation Radiation) technique is a well suited method for the investigation of the electronic structure, in particular the fermiology of correlated systems. Measuring the two dimensional projection of the two-photon-momentum-distribution of the annihilation radiation the three dimensional electron momentum distribution can be calculated via tomographic reconstruction. A new 2D-ACAR spectrometer is currently being installed at the NEPOMUC facility at the research reactor in Garching. In the setup, the positrons from a 50 mCi ²²Na source are guided onto the sample by an axial magnetic field created by a normal conducting electromagnet. The use of especially developed soft iron pole caps, guarantees a homogeneous magnetic field with a magnetic flux density > 1.2 T while allowing axial access to the sample- and positioning stage. The sample stage itself can be cooled by a standard cryo-cooler to temperatures below 30 K in order to reduce the smearing of the angular resolution by the positron momentum. The key features of the new spectrometer are presented. In addition, first results of measurements on a intermetalic Heussler crystal are discussed and compared with first principle band structure calculations.