Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...

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$Planungsraster FP C SoSe2013 Di. 13:30-18:00 h Gruppe \ Tag 9.4 ...$

Posters Monday February 4 Poster 15: Mechanism for Giant Thermopower in Negative-U Molecular Quantum Dots Theo Costi We investigate with the aid of numerical renormalization group techniques the thermoelectric properties of a molecular quantum dot described by the negative-U Anderson model. We show that the charge Kondo effect provides a mechanism for enhanced thermoelectric power via a correlation-induced asymmetry in the spectral function close to the Fermi level. We show that this effect results in a dramatic enhancement of the Kondo-induced peak in the thermopower of negative-U systems with Seebeck coefficients exceeding 50 µV/K over a wide range of gate voltages [1,2]. [1] S. Andergassen, T. A. Costi and V. Zlatic, Phys. Rev. B 84, 241107 (R) (2011) [2] T. A. Costi and V. Zlatic, Phys. Rev. Lett. {bf 108}, 36402 (2012); in "New Materials for Thermoelectric Applications: Theory and Experiment", ed. V. Zlatic and A. C. Hewson, ISBN 978-94-007-4983-2 (Springer, Berlin, 2012) Coauthors: S. Andergassen and V. Zlatic Poster 16: Boltzmann-type approach to thermal drag in spin-1/2-ladder systems coupled to phonons Christian Bartsch We quantitatively investigate the spin-phonon drag contributions to the thermal conductivity of a two-leg-spin-1/2-ladder coupled to lattice vibrations in a magnetoelastic way. By applying suitable transformations the system is mapped onto a weakly interacting quantum gas model of bosonic spin excitations (magnons) and phonons. We adequately construct a collision term of a linear(ized) Boltzmann equation from the underlying quantum dynamics by means of a pertinent projection operator technique. From the Boltzmann equation we obtain concrete numerical values for the drag conductivity and relate it to the individual thermal conductivities of magnons and phonons for parameter ranges which are typical for certain material classes. 68
Posters Monday February 4 Poster 17: Rashba spin-orbit interaction in a quantum wire superlattice Sigurdur I. Erlingsson We study the effects of a longitudinal periodic potential on a parabolic quantum wire, and long quantum point contacts, defined in a two-dimensional electron gas with Rashba spin-orbit interaction. For an infinite wire superlattice we find that the energy gaps are shifted away from the usual Bragg planes due to the Rashba spin-orbit interaction. We have also calculated the charge conductance through a periodic potential of a finite length via the nonequilibrium Green’s function method combined with the Landauer formalism. We find dips in the conductance that correspond well to the energy gaps of the infinite wire superlattice. From the infinite wire energy dispersion, we derive an equation relating the location of the conductance dips as a function of the Fermi energy to the Rashba spin-orbit coupling strength. We propose that the strength of the Rashba spin-orbit interaction can be extracted via a charge conductance measurement. Poster 18: Electronic states in a cylindrical nanowire in magnetic and electric fields Andrei Manolescu Single particle states of electrons situated on a closed cylindrical surface of radius 30-100 nm are calculated. The length of the cylinder may be either infinite or finite. In the presence of a magnetic field uniform in space, but perpendicular to the longitudinal axis of the cylinder, the orbital effects depend on the radial component of the magnetic field. For a sufficiently strong field, when the magnetic length becomes comparable to the radius of the cylinder, the orbital motion corresponds to closed cyclotron orbits in the regions with strong radial field, but to open quasi one-dimensional snaking orbits in the regions where the radial field vanishes and changes sign. The energy of the cyclotron states increases with the magnetic field relatively to the energy of the snaking states such that at high magnetic fields the electrons concentrate around the snaking orbits. The spin of the electron is included via Zeeman and Rashba spin-orbit effects. A uniform electric field perpendicular to the cylinder is also considered, as being produced by a metallic electrode placed near the cylinder. In this case the spin-orbit coupling becomes anisotropic. Attempts to include Coulomb effects in the Hartree-Fock approximation are discussed. 69
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PROGRAM BOOK International workshop
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What comes with this booklet With t
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Getting to the institute (1) If you
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Workshop lecture hall • The works
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Lunch information Lunch will be tak
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Talks Monday February 4 Talk progra
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Talks Monday February 4 Notes 13
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Talks Monday February 4 Notes 15
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Page 29 and 30: Talks Tuesday February 5 Talks Tues
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Page 47 and 48: Talks Wednesday February 6 Talks We
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Page 86 and 87: 18. Domenico Giuliano, Universita
Page 88 and 89: 55. Jens Paaske, Copenhagen Univers
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Workshop book - Physikzentrum der RWTH Aachen - RWTH Aachen ...

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