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Doktorsvörn - Kristinn Torfason

Variations on Transport for a Quantum Flute

  • 22.3.2013, 14:00 - 15:00

Kristinn Torfason will defend his Ph.D. thesis: "Variations on Transport for a Quantum Flute" Friday, March 22 at 14:00 in Askja 132 at the University of Iceland.

Kristinn Torfason is the first joint Ph.D. candidate of the University of Iceland and Reykjavik University to defend his thesis. His supervisors are Prof. Viðar Guðmundsson at the University of Iceland and Prof. Andrei Manolescu at the Reykjavik University. Other members of this doctoral committee are Prof. Hannes Jónsson at the University of Iceland, and Asc. Prof. Sigurður I. Erlingsson at the Reykjavik University.

Opponents will be: Prof. David Sánchez at the Institute for Cross-Disciplinary Physics and Complex Systems (IFISC) at the Universitat de les Illes Balears, Palma de Mallorca, and Prof. Piroz Zamankhan at the Faculty of Industrial Engineering, Mechanical Engineering and Computer at the University of Iceland.

Professor Hafliði Pétur Gíslason, Dean of the Faculty of Physical Sciences, University of Iceland, will preside at the ceremony, which will take place in room 132 in Askja, and commences at 14:00.

Kristinn Torfason is born in Iceland 1984. He completed both B.Sc. and M.Sc. degrees in physics from the University of Iceland. His research has been supported by the Icelandic Research and Instruments Funds and the Development Fund of the Reykjavik University.


A time-dependent Lippmann-Schwinger scattering model is used to study the transport of a time-modulated double quantum point contact system in the  presence of perpendicular magnetic field. The conductance through the system is calculated using the Landauer-Büttiker framework. An observed
magnetic field induced Fano resonance is seen in the conductance. A Generalized Master Equation (GME) is then used to describe the non-equilibrium time-dependent transport through a similar system, a short quantum wire connected to semi-infinite leads. A lattice model is used to described the leads and system, with the Coulomb interaction between the electrons in the sample included via the exact diagonalization method. The contact coupling strength between the leads and the wire is modulated by out-of-phase time-dependent potentials that simulate a turnstile device. The placement of one of the leads is fixed while the position of the other is varied. The propagation of both sinusoidal and rectangular pulses is examined. The current profiles in both leads are found to depend on not only the shape of the pulses, but also the position of the contacts. The current reflects standing waves created by the contact potentials, like in a wind musical instrument (for example, a flute). Finally thermoelectric currents through a quantum dot are studied in both the transient and steady-state regime using the GME. The two semi-infinite leads are kept at the same chemical potential but at different temperatures to produce a thermoelectric current, which has a varying sign depending on the chemical potential. A saw-tooth like profile is observed in the current along with plateaus of zero current.

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