quantum transport; quantum electronics; mesoscopic physics; nanoelectronics; spintronics; Andreev reflection; Cooper-pair splitter; carbon nanotubes; semicondcuting nanowires; graphene; nano devices
F. Freitag M. Weiss R. Maurand J. Trbovic and C. Schönenberger, Weiss M., Schönenberger C. (2013), Spin Symmetry of the Bilayer Graphene Groundstate, in Phys. Rev. B
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J. Schindele A. Baumgartner and C. Schönenberger (2012), Near-Unity Cooper-pair Splitting Efficiency, in Phys. Rev. Lett.
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F. Freitag M. Weiss R. Maurand J. Trbovic and C. Schönenberger (2012), Homogeneity of Bilayer Graphene, in Solid State Communications
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Freitag Frank, Trbovic J., Schönenberger C., Schönenberger C. (2012), Graphene: From Diffusive to Ultraclean-Interacting Systems
Freitag F., Csonka S., Baumgartner A., Fülöp G., d'Hollosy S., Nygard J., Schönenberger C. (2012), Spontaneously Gapped Ground State in Suspended Bilayer Graphene, in Phys. Rev. Lett.
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Aurich Hagen (2011), Carbon Nanotube Spin-Valve with Optimized Ferromagnetic Contacts
Hofstetter L. (2011), Finite bias Cooper pair splitting, in Phys Rev. Lett.
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Freitag F. (2011), Conductance fluctuations in graphene devices with superconducting contacts in different charge density regimes, in Phys. Status Solidi B (arXiv:1108.4599)
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Hofstetter Lukas, Csonka S., Baumgartner A., Fülöp G. (2011), Hybrid Quantum Dots in InAs
Eichler A., Trbovic J., Schönenberger C. (2011), Gate-tunable split Kondo effect in a carbon nanotube quantum dot, in Nanotechnology
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The ever growing interest in low dimensional systems, such as one-dimensional wires and zero-dimensional quantum dots, is due to the unique properties of charge and spin currents in such systems. Over the last years, we have been very successful in using carbon nanotubes, graphene and in particular semicondcuting nanowires to realize devices with unique contact topologies, enabling to explore new physical phenomena, such as non-local Andreev reflection, the ferromagnetic contact induced exchange coupling to a quantum dot, supercurrent in a quantum dot with Kondo correlations, spin transport through quantum dots and conductance fluctuations in graphene.A very striking result has been the realization of a Cooper pair splitter, see Hofstetter et al. Nature V461, p960 (2009). Making use of confinement and Coulomb blockade in quantum dots, we have shown that the two electrons of individual Cooper-pairs can be split. Though very exciting, this is only the first step. The goal is to demonstrate that this principle provides an efficient source of entangled EPR pairs of electrons. To do so, one has to measure the entanglement, which is a very challenging task, and than see how one can reach the largest possible pair current without loosing the entanglement.We will first explore the physics of the splitting in more depth. We will add ferromagnetic contacts which will allow spin projection measurements. Combing this with noise-correlation experiments provides a means for a Bell-state measurement with which the entanglement can be assessed. To insure that Cooper-pairs are split one by one and that pairs can be launched on ``demand'', one has to either increase the superconducting gap or lower the tunneling coupling from the superconductor to the quantum dots. We will explore both avenues by testing superconductors with a higher transition temperature (e.g. Nb and NbN) and define additional contact barriers withbottom-and/or top gates. As a basis for the quantum dots we will be using InAs nanowires, carbon nanotubes and graphene. At the core of our research are therefore low-dimensional hybrid devices, which are obtained through a combination of contacts employing normal metals, superconductors and ferromagnets.This provides a large space in which novel phenomena in correlated spin and charge transport emerge. We just mention the recent discovery of topological insulators, which appear in so-called inverted small band-gap materials. A similar state can also be generated in one-dimensional conductors with strong spin-orbit interaction (e.g. InAs and InSb) when ferromagnetic and superconducting contacts are added.Information on the group can be found under: www.nanoelectronics.ch