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Björn Kubala1,2, Zoltán Ádám Németh1,3, Jürgen König2, and Yuval Gefen3
1 Physics Department, ASC, and CeNS, Ludwig-Maximilians-Universität, Theresienstrasse 37, 80333 Munich, Germany 2 Institut für Theoretische Physik III, Ruhr-Universität Bochum, 44780 Bochum, Germany 3 Department of Condensed Matter Physics, The Weizmann Institute of Science, 76100 Rehovot, Israel We study the occupation of two electrostatically-coupled single-level quantum dots with spinless electrons. If a single-particle picture holds a change of the gate voltage can be described by a rigid shift of the single-particle spectrum, and levels are filled 'one by one', yielding standard Coulomb-blockade effects. Here, however, the interplay of strong Coulomb interaction, as usually present in small semiconductor quantum dots, and of electron tunneling between dot levels and leads can become manifest in nontrivial Coulomb correlations. This results in a nonmonotonic filling of the individual levels. We use a diagrammatic imaginary-time technique that is exact in the charging energy but perturbative in the tunnel coupling. Extending previous work [1] we go to second order in the dot-lead coupling strength, respectively the level width. Such higher order calculation, firstly, allows an investigation of interference of the different tunneling paths that are possible if the two quantum dots are coupled to two common reservoirs in an Aharonov-Bohm interferometer geometry. Secondly, the regime where quantum fluctuations in the occupation of one level are governed by quantum fluctuations on the other level can be explored. The latter results in a crossover in the width of the nonmonotonicity from thermal broadening to a quantum fluctuation dominated dependence. [1] J. König and Y. Gefen, Phys. Rev. B 71, 201308(R) (2005). |
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