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End date: 2019 × Start date: 2016 × DDC: 530 × Type: article × Version: publishedVersion × search.filters.applied.f.series: New Journal of Physics, Volume 14 ×

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Now showing 1 - 4 of 4
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    A semiconductor laser system for the production of antihydrogen
    (Milton Park : Taylor & Francis, 2012) Müllers, A.; Böttner, S.; Kolbe, D.; Diehl, T.; Koglbauer, A.; Sattler, M.; Stappel, M.; Steinborn, R.; Walz, J.; Gabrielse, G.
    Laser-controlled charge exchange is a promising method for producing cold antihydrogen. Caesium atoms in Rydberg states collide with positrons and create positronium. These positronium atoms then interact with antiprotons, forming antihydrogen. Laser excitation of the caesium atoms is essential to increase the cross section of the charge-exchange collisions. This method was demonstrated in 2004 by the ATRAP collaboration by using an available copper vapour laser. For a second generation of charge-exchange experiments we have designed a new semiconductor laser system that features several improvements compared to the copper vapour laser. We describe this new laser system and show the results from the excitation of caesium atoms to Rydberg states within the strong magnetic fields in the ATRAP apparatus.
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    Surface and bulk electronic structure of the unconventional superconductor Sr2RuO4: Unusual splitting of the β band
    (Milton Park : Taylor & Francis, 2012) Zabolotnyy, V.B.; Carleschi, E.; Kim, T.K.; Kordyuk, A.A.; Trinckauf, J.; Geck, J.; Evtushinsky, D.; Doyle, B.P.; Fittipaldi, R.; Cuoco, M.; Vecchione, A.; Büchner, B.; Borisenko, S.V.
    We present an angle-resolved photoemission study of the surface and bulk electronic structure of the single layer ruthenate Sr2RuO4. As the early studies by photoemission and scanning tunneling microscopy were confronted with a problem of surface reconstruction, surface ageing was previously proposed as a possible remedy to access the bulk states. Here, we suggest an alternative way by demonstrating that, in the case of Sr2RuO4, circularly polarized light can be used to disentangle the signals from the bulk and surface layers, thus opening the possibility to investigate many-body interactions both in bulk and surface bands. The proposed procedure results in improved momentum resolution, which enabled us to detect an unexpected splitting of the surface β band. We discuss the origin of the splitting of the β band and the possible connection with the Rashba effect at the surface.
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    Stimulated emission and absorption of photons in magnetic point contacts
    (Milton Park : Taylor & Francis, 2012) Naidyuk, Yu G.; Balkashin, O.P.; Fisun, V.V.; Yanson, I.K.; Kadigrobov, A.; Shekhter, R.I.; Jonson, M.; Neu, V.; Seifert, M.; Korenivski, V.
    Point contacts between high anisotropy ferromagnetic SmCo5 and normal metal Cu are used to achieve a strong spin-population inversion in the contact core. Subjected to microwave irradiation in resonance with the Zeeman splitting in Cu, the inverted spin population relaxes through stimulated spin-flip photon emission, detected as peaks in the point-contact resistance. Resonant spin-flip photon absorption is detected as resistance minima, corresponding to sourcing the photon field energy into the electrical circuit. These results demonstrate fundamental mechanisms that are potentially useful in designing metallic spin-based lasers.
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    Mechanism of non-classical light emission from acoustically populated (311)A GaAs quantum wires
    (Milton Park : Taylor & Francis, 2012) Lazić, S.; Hey, R.; Santos, P.V.
    We employ surface acoustic waves (SAWs) to control the transfer of photo-generated carriers between interconnected quantum wells and quantum wires (QWRs) grown on pre-patterned (311)A GaAs substrates. Optical studies, carried out under remote acoustic excitation of a single QWR, have shown sharp photoluminescence lines and antibunched photons with tunable emission energy. These features are attributed to recombination of acoustically transported carriers in potential inhomogeneities within the wire. The origin of the photon antibunching is discussed in terms of a 'bottleneck' in the number of carriers trapped in the QWR, which restricts the number of recombination events per SAW cycle. We propose a model for antibunching based on the trapping of carriers induced by the SAW piezoelectric field in states at the interface between the GaAs QWR and the AlGaAs barriers. Non-classical light is emitted during the subsequent release of the trapped carriers into the recombination centers within the wire. The spatial distribution of the emitting recombination centers is estimated using time-resolved measurements.