[{"type":"speech","title":"Co-tunneling effects in transport through interacting quantum dots","issued":{"date-parts":[["2007"]]},"author":[{"family":"Aghassi","given":"J."},{"family":"Hettler","given":"M."},{"family":"Sch\u00f6n","given":"G."}],"note":"71.Jahrestagung der Deutschen Physikalischen Gesellschaft und DPG Fr\u00fchjahrstagung des Arbeitskreises Festk\u00f6rperphysik, Fachverband Tiefe Temperaturen, Regensburg, 26.-30.M\u00e4rz 2007 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.42(2007) TT 18.2","abstract":"Section Low Temperature Physics (TT)\nWednesday\nWe apply an antiferromagnetic symmetry breaking implementation of\nthe dynamical cluster approximation (DCA) to the two-dimensional\nhole-doped Kondo lattice model with hopping t and coupling J.\nPrecise calculations of single particle spectral functions compare well\nwith exact BSS results at the particle-hole symmetric point. However,\nour DCA version, combined with a QMC cluster solver, also allows\nsimulations away from particle-hole symmetry and has enabled us to\nmap out the magnetic phase diagram of the model as a function of\ndoping, coupling J\/t and band structure.\nAt half-\ufb01lling, our results show that the linear behaviour of the\nquasi-particle gap at small values of J\/t is a direct consequence of\nparticle-hole symmetry, which leads to nesting of the Fermi surface.\nBreaking the symmetry, by inclusion of a diagonal hopping term, results in a greatly reduced gap which appears to follow a Kondo scale.\nUpon doping the magnetic phase observed at half-\ufb01lling survives and\nultimately gives way to a paramagnetic phase. Across this magnetic\norder disorder transition, we track the topology of the Fermi surface.\nTT 17.15\nWed 17:45\nH18\n\u00a8\nTime: Wednesday 14:00\u201317:15\nLocation: H19\nTT 18.1\nWed 14:00\nH19\nCharge transfer statistics through multi-terminal Kondo and\nAnderson impurities \u2014 \u2022Andrei Komnik1 , Thomas Schmidt1 ,\n\u2014 2 Department of Mathematics, Imperial College London, 180\nQueen\u2019s Gate, London SW7 2AZ, United Kingdom\nWe investigate the charge transfer statistics through a quantum dot in\nthe Kondo regime coupled to an arbitrary number of terminals. Using the e\ufb00ective Hamiltonian valid at energies far below the Kondo\ntemperature we calculate the generating function for the full counting\nstatistics (FCS) perturbatively in the leading irrelevant operators. The\ntransport seems to be mediated not only by single electron tunnelling\nbut by correlated transport of electron pairs as well. We propose a\nmeasurement of cross correlations of Hanbury Brown and Twiss type\nin a multi-terminal geometry which is able to explicitly discern both\nprocesses in experiments. Furthermore we make predictions for generalised Fano factors to be universal and parameter-free. By comparison\nof perturbative expansions for weak and strong couplings we make\npredictions for the FCS of a more realistic multi-terminal Anderson\nimpurity model, which are valid at all energy scales as long as the\napplied transport voltage is small.\nTT 18.2\nWed 14:15\nH19\nCo-tunneling e\ufb00ects in transport through interacting quantum dots \u2014 \u2022Jasmin Aghassi1,2 , Matthias Hettler1 , and Gerd\n\u00a8\n76201 Karlsruhe \u2014 2 Institut f\u00a8 r theoretische Festk\u00a8rperphysik, Uniu\nversit\u00a8t Karlsruhe, 76128 Karlsruhe\nWe study charge transport in quantum dot systems within a diagrammatic technique. The current-voltage characteristics as well as\nthe current noise are calculated within second-order perturbation expansion in the coupling parameter \u0393. We allow for an intermediate\ncoupling regime up to coupling constants of \u0393 = kB T , where kB is the\nBoltzmann constant and T the temperature. We explicitly account\nfor intra- and inter-dot Coulomb interactions and the resulting manybody states of the quantum dots. For a single multilevel quantum dot\nwe investigate the co-tunneling e\ufb00ects on the conductance and noise of\nthe system in dependence of an applied gate voltage. In the Coulomb\nblockade region super-Poissonian noise is observed at the inelastic\nco-tunneling energy scale. This energy scale is also observable in the\nconductance in some cases. For non-local systems such as chains of\ncoupled quantum dots (\u201carti\ufb01cial molecules\u201d) sequential tunneling\nresults for transport under asymmetric conditions, i.e. non-resonant\ndots or asymmetric couplings are compared to second order results.\nA. Thielmann et.al., Phys. Rev. Lett., 95, 146806 (2005)\nJ. Aghassi et.al, Appl. Phys. Lett. 89, 052101 (2006), Phys. Rev.B\n73, 195323 (2006)\nTT 18.3\nWed 14:30\nH19\nFrequency dependent quantum shot noise \u2014 \u2022Jan C. Ham-\nmer and Wolfgang Belzig \u2014 University of Konstanz, Department\nof Physics, 78457 Konstanz, Germany\nWe study frequency-dependent quantum shot noise in the coherent\ncharge transport through a double barrier quantum dot. In the framework of the scattering formalism we show how electron transport\nthrough such a Fabry-Perot-like setup reveals a super-Poissonian and\nan asymmetric noise spectrum for large frequencies. It depends on\nthe applied bias voltage, the structure of the energy levels inside the\nscattering region and the coupling to the leads. For example, well separated energy levels lead to steps in the noise due to the emission and\nabsorption of photons which get washed out as the width of the levels\nbroadens. These can be shifted with respect to frequency by varying\na gate voltage. At low frequency the Fano factor gets reduced and the\nspectrum is found to be symmetric.\nTT 18.4\nWed 14:45\nH19\nGeneration of Nonlocal Spin Entanglement in Nonequi\u00a8\n\u00a8\n\u00a8\nGuido Burkard3 , and Gerd Schon1 \u2014 1 Institut f\u00a8 r Theoretisu\nche Festk\u00a8rperphysik and DFG-Center for Functional Nanostructures\n(CFN), Universit\u00a8t Karlsruhe \u2014 2 Institut f\u00a8 r Theoretische Physik III,\nRuhr-Universit\u00a8t Bochum \u2014 3 Department of Physics and Astronomy,\nUniversity of Basel\nWe propose schemes for generating nonlocal spin entanglement in systems of two quantum dots with onsite Coulomb repulsion weakly coupled to a joint electron reservoir. In nonequilibrium situations with\none extra electron on each dot, we \ufb01nd the double-dot system in socalled Werner states with a \ufb01delity exceeding 1\/2, which indicates spin\nentanglement. We consider two speci\ufb01c setups. In the \ufb01rst setup we\nstudy the transient behavior of the system after rapidly pushing the\ndot levels from above to below the Fermi energy of the joint lead. We\n\ufb01nd the formation of an enhanced probability of the singlet state as\ncompared to the triplet. In the second setup we analyze the stationary\nstate with an applied bias voltage between the joint reservoir and two\nadditional leads, which are weakly coupled to the dots. Depending on\nthe polarity of the bias, we \ufb01nd an enhanced probability for either the\nsinglet or the triplet states.\nTT 18.5\nWed 15:00\nH19\nNon-equilibrium Josephson current through interacting\nquantum dots \u2014 \u2022Marco G. Pala1 , Michele Governale2 , and\n\u00a8\n\u00a8\nUniversit\u00a8t Bochum, D-44780 Bochum, Germany\nWe study transport through a quantum dot weakly coupled to both\nnormal and superconducting leads. To this aim, we generalize a diagrammatic real-time transport theory[1] to account for superconductivity in the leads. In particular, we consider a system consisting of a\nquantum dot tunnel coupled to one normal and two superconducting\nleads. A \ufb01nite voltage can be applied between the normal and the\nsuperconducting leads to drive the dot out","kit-publication-id":"230067493"}]