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Statut |
Confirmé |
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Série |
LPENS-MDQ |
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Domaines |
cond-mat |
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Date |
Mardi 28 Juin 2016 |
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Heure |
14:00 |
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Institut |
LPA |
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Salle |
Conf IV, 24 rue Lhomond |
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Nom de l'orateur |
Baranger |
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Prenom de l'orateur |
Harold |
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Addresse email de l'orateur |
baranger [at] phy [dot] duke [dot] edu |
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Institution de l'orateur |
Department of Physics, Duke University |
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Titre |
Tunneling Through Quantum Dots in a Dissipative Environment: Quantum Critical Behavior |
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Résumé |
Despite the ubiquity of quantum phase transitions (QPT) in contemporary theoretical physics, obtaining clear experimental signatures has been challenging. I start by presenting a recent experiment in which it was possible to thoroughly characterize a QPT caused by coupling to an environment. The system is a single-molecule transistor built from a carbon nanotube quantum dot connected to strongly dissipative contacts. The electrical conductance of this system is highly singular at low temperature: the conductance is 0 except at one special point (on resonance and symmetric coupling) at which electrons are fully transmitted with unit probability-- this is the quantum critical point.
I then turn to the theoretical understanding of this QPT obtained by mapping the problem onto that of a resonant Majorana fermion level in an interacting electron liquid. The unitary transmission obtained in the experiment is seen as a competition between the two leads, as in the two-channel Kondo problem. The deviations from unitarity at nonzero temperature are connected to residual interactions among the Majoranas.
Finally, I present theoretical results for tunneling through two quantum dots in the Kondo regime, a system which potentially has an interesting intermediate fixed point (that of the two-impurity Kondo model). While the normal tendency of dissipation is to destroy interesting many-body correlations, we show that in this case coupling to the bath stabilizes the intermediate fixed point and renders it experimentally observable. |
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Numéro de preprint arXiv |
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