Institute of Nanotechnology

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Wednesday, 22 January 2014
13:30 
Cooper-Pair Splitting and Spectroscopy in Double Quantum Dot Devices with Superconducting Charge Injector
Colloquium
Prof. Christian Schönenberger, Uni Basel, Nanoelectronics

Talk given by Prof. Christian Schönenberger An elegant idea for the creation of entangled electrons in a solid-state device is to split Cooper pairs, which are in a spin singlet state, by coupling a superconductor to two parallel quantum dots (QDs) in a Y-junction geometry [1]. Cooper pair splitting (CPS) was investigated recently in devices based on InAs nanowires [2,3] and carbon nanotubes (CNTs) [4,5] and identified by a positive correlation between the currents through the QDs. I will first discuss recent experiments that demonstrate high splitting efficiencies > 90%. A high CPS efficiency is a prerequisite for Bell state measurements, a clear way of proving that Cooper pairs can be extracted coherently and lead to spatially separated entangled electron pairs. Further requirements on entanglement measurements will be addressed in the talk as well. I will then continue to discuss new results in semiconducting nanowires with Nb contacts that display a great variety of correlations. Using also Nb as the injector another distinct experiment with CNT devices will be discussed. In the regime of a strong tunnel coupling between the QDs and superconducting contact, the CPS efficiency is expected to be small [5]. However, the superconducting proximity effect can support so-called Andreev bound states (ABS) on a QD, which can be detected by conventional transport spectroscopy [6]. Here we use a Niobium contacted CNT Cooper pair splitter and investigate the response of the ABS formed on one QD to CPS. We find an appreciable non-local conductance when the bias is large enough to excite charge fluctuations in the ABS. These non-local signals change sign with opposite bias and, more intriguingly, when the ABS ground state changes from a spin singlet to a doublet. Our experiments can be understood qualitatively in an intuitive picture for ABS and CPS and show that CPS can be used as a tool to investigate complex hybrid nanoelectronic structures. This is a collaborative effort with the groups of Szabolcs Csonka, Budapst University of Technology and Economy, Jesper Nygard, Nano-Science Center, Niels Bohr Institute of the University of Copenhagen, and Jan Martinek- IFM-PAN, Poznan, Polen. I acknowledge funding from the Swiss NFS, SNI , NCCR-QSIT, FP7-SE2ND and ERC-QUEST. References [1] P. Recher, E.V. Sukhorukov and D. Loss, Phys. Rev. B 63, 165314 (2001). [2] L. Hofstetter, S. Csonka, J. Nygård and C. Schönenberger, Nature 461, 960 (2009). [3] L. Hofstetter, S. Csonka, A. Baumgartner, G. Fülöp S. d’Hollosy, J. Nygård and C. Schönenberger, Phys. Rev. Lett. 107, 136801 (2011). [4] L.G. Herrmann, F. Portier, P. Roche, A. Levy Yeyati, T. Kontos and C. Strunk, Phys. Rev. Lett. 104, 026801 (2010). [5] J. Schindele, A. Baumgartner, and C. Schönenberger, Phys. Rev. Lett. 109, 157002 (2012). [6] J.-D. Pillet, C.H.L. Quay, P. Morfin, C. Bena, A. Levy Yeyati and P. Joyez, Nature Phys. 6, 965 (2010).

16:30 
Functional Nanomaterials: Synthesis, Properties, Application
Colloquium
Prof. Claus Feldmann

This presentation addresses the synthesis and characterization of selected nanomaterials, including less-noble metals, inorganic-organic hybrids, and hollow spheres. These nanomaterials are prepared via polyol-mediated synthesis, microemulsion techniques, ionic liquids and aqueous precipitation. Materials-related properties and potential areas of application relate to nanoscale luminescent materials, nanocontainers for biomedical issues, gas sorption and gas separation, catalysis/photocatalysis and thin-film solar cells. A current example of our synthesis activities is illustrated with the following scheme:

Wednesday, 29 January 2014
16:30 
Metadynamics for Computational Heterogeneous Catalysis
Colloquium
Prof. Bernd Meyer, FAU Erlangen-Nürnberg, Interdisciplinary Center for Molecular Materials (ICMM) and Computer-Chemistry-Center (CCC)

Talk given by Prof. Bernd Meyer Although methanol synthesis from CO and H2 over ZnO catalysts is a rather simple chemical reaction, the interplay of physical and chemical processes at the ZnO surfaces give rise to a complex free energy landscape. The preferred charge state of oxygen vacancies is dictated by the chemical composition and the thermodynamic properties of the gas phase in contact with ZnO. In turn, reaction intermediates and pathways along the catalytic cycle taking place at or close to these defects depend in a sensitive way on their oxidation state. Instead of constructing the potential energy landscape for this reaction 'by hand' using static DFT and NEB calculations as traditionally done, it will be shown that the underlying complex reaction network from CO to methanol can be generated based on ab-initio metadynamics simulations. In addition to be able to `synthesize' all previously discussed reaction intermediates, novel species are found and mechanistic insights into the reaction network of this surface chemical reaction are obtained by a global exploration of the free energy landscape. In a second step, the global picture is refined by investigating individual reaction pathways, taking into account different charge states of the oxygen vacancies. Finally, first insights into the structure and reactivity of the much more complex Cu/ZnO catalyst, which is subject to so-called 'strong metal support interactions' (SMSI), will be presented.

Wednesday, 05 February 2014
13:00 
Efficient Macromolecular Ligation Chemistries for Nano- and Micro-Object Functionalization and Photoresist Design
Colloquium
Prof. Christopher Barner-Kowollik, Karlsruher Institut für Technologie, Institut für Technische Chemie und Polymerchemie, Lehrstuhl für Präparative Makromolekulare Chemie

Talk given by Prof. Christopher Barner-Kowollik This lecture will highlight our most recent progress in the development of versatile, efficient and mild protocols for the functionalization of a wide variety of nano- and micro-objects, including fullerenes and carbon nanotubes with precision engineered functional macromolecules. The employed polymers include stimuli-responsive systems as well as conducting polymers. In addition, novel avenues for the design of reactive photo-resists for direct laser writing applications will be discussed in detail. The synthetic efforts are underpinned by in-depth molecular surface characterization methodologies, allowing for a quantitative analysis of the prepared hybrid materials.

Monday, 17 February 2014
 
Surface-Confined Synthesis of Nanostructures, Winter School
Conference
Hotel Magnetberg Baden-Baden
Scheibenstrasse 18 …

The winter school will cover all areas related to surface-confined synthesis of molecular nanostructures (covalent C-C coupling reactions, supramolecular self-assembly, graphene and graphene-like 2D materials, implementation and integration of molecular nanostructures into nanosystems including photonics, spintronics, bioresponse, etc.). Target audience -Ph.D. students from France and Germany -young postdocs working at the interface of materials science, surface physics and chemistry Further details: http://www.int.kit.edu/ruben_events.php
Sponsor: French-German University, Université Franco-Allemande (UFA)

Tuesday, 18 February 2014
 
Surface-Confined Synthesis of Nanostructures, Winter School
Conference
Hotel Magnetberg Baden-Baden
Scheibenstrasse 18 …

The winter school will cover all areas related to surface-confined synthesis of molecular nanostructures (covalent C-C coupling reactions, supramolecular self-assembly, graphene and graphene-like 2D materials, implementation and integration of molecular nanostructures into nanosystems including photonics, spintronics, bioresponse, etc.). Target audience -Ph.D. students from France and Germany -young postdocs working at the interface of materials science, surface physics and chemistry Further details: http://www.int.kit.edu/ruben_events.php
Sponsor: French-German University, Université Franco-Allemande (UFA)

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