Transport durch normal- und supraleitende Quanten-Punktkontakte mit komplexer elektronischer Struktur
Zusammenfassung der Projektergebnisse
A broad range of aspects of spectral structure and transport through interacting point contact systems has been investigated, ranging from strogly correlated multi-orbital quantum impurities to non-equilibrium phase transitions and the transport in superconducting Kondo Qdot devices and non-equilibrium Josephson oscillations in trapped Bose-Einstein condensates. The two highlights of the results are : (1) We put forward a model of a three-level quantum impurity with partially broken SU(3) symmetry embedded in a metal, which may be realized by a heavy, charged particle bound in the interstitial space of a host lattice. It was shown by renormalization group calculations that this model has a stable two-channel Kondo (2CK) fixed point for a wide range of parameters. It is the first realistic model to exhibit non-Fermi liquid 2CK behavior without fine tuning of parameters, which explains at the same time the sharp spikes of the differential conductance observed in related experiments on ultrasmall quantum point contacts. (2) The time evolution of Josephson oscillations in a Bose-Einstein condensate trapped in a double well potential far from equilibrium was analyzed using non-equilibrium quantum field theory. Rich dynamics were found, exhibiting a highly non-linear transition from slow undamped Josephson oscillations of the BEC to fast Rabi oscillations of the Bogoliubov quasiparticle system. The damping of the oscillations and ultimate equilibration of the isolated system at an elevated temperature are controlled by three distinct time scales.
Projektbezogene Publikationen (Auswahl)
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Conductance Quasi-quantization of Quantum Point Contacts: Why Tight Binding Models are Insufficient. In Anderson Localization and
its Ramifications, T. Brandes and S. Kettemann Eds.
(Lecture Notes in Physics, 630) pp 303-315, 2004, Springer, Berlin, Heidelberg, New York
S. Kirchner, J. Kroha, P. Wölfle and E. Scheer
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Conserving Diagrammatic Approximations for Quantum Impurity Models: NCA and CTMA. Invited article on the occasion of the 40th anniversary of the discovery of the Kondo effect 1964.
Journal of the Physical Society of Japan, 74 (1), pp.16-26 (2005)
J. Kroha and P. Wölfle
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π-Junction Behavior and Andreev Bound States in Non-dissipative Kondo Point Contacts with Superconducting Leads.
Physical Review B, 72: 174502 (2005) and in Virtual Journal of Applications of Superconductivity, 9(10) (2005)
G. Sellier, T. Kopp, J. Kroha, Y. Barash
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Spin Correlations and Finite-Size Effects in the Kondo Box.
Physical Review Letters, 97: 136604 (2006)
Th. Hand, J. Kroha, H. Monien
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Stable Two-channel Kondo Fixed Point of an SU(3) Quantum Defect in a Metal: Renormalization Group Analysis and Conductance Spikes.
Physical Review Letters, 99 (18): 186601 (2007)
M. Arnold, T. Langenbruch, J. Kroha
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Strong vs. Weak Coupling Duality and Couphng Dependence of the Kondo
Temperature in the Two-Channel Kondo Model.
Physical Review B, 75(4), 045129 (2007)
Ch. Kolf, J. Kroha
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Universality in Voltage-driven Non-equilibrium Phase Transitions.
Dedicated to Prof. H. v. Löhneysen on the occasion of his 60th birthday. Journal of Low Temperature Physics, 147 (3-4), pp. 505-515 (2007)
Johann Kroha, Michael Arnold and Beate Griepernau
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Nonequilibrium Josephson oscillations in Bose-Einstein condensates without dissipation.
Physical Review Letters, 103(10): 105302 (2009)
Mauricio Trujillo Martinez, Anna Posazhennikova, Johann Kroha
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Nonequilibrium Josephson oscillations in Bose-Einstein condensates with quasiparticle damping. International Workshop and Summer School
Quo Vadis Bose-Einstein Condensation?, Dresden, 02-20 August, 2010.
Johann Kroha
