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Abstract: We study correlated two-level quantum dots, coupled in effective 1-channelfashion to metallic leads; with electron interactions including on-level andinter-level Coulomb repulsions, as well as the inter-orbital Hund-s ruleexchange favoring the spin-1 state in the relevant sector of the free dot. Forarbitrary dot occupancy, the underlying phases, quantum phase transitionsQPTs, thermodynamics, single-particle dynamics and electronic transportproperties are considered; and direct comparison is made to conductanceexperiments on lateral quantum dots. Two distinct phases arise generically, onecharacterised by a normal Fermi liquid fixed point FP, the other by anunderscreened USC spin-1 FP. Associated QPTs, which occur in general in amixed valent regime of non-integral dot charge, are found to consist ofcontinuous lines of Kosterlitz-Thouless transitions, separated by first orderlevel-crossing transitions at high symmetry points. A `Friedel-Luttinger sumrule- is derived and, together with a deduced generalization of Luttinger-stheorem to the USC phase a singular Fermi liquid, is used to obtain a generalresult for the T=0 zero-bias conductance, expressed solely in terms of the dotoccupancy and applicable to both phases. Relatedly, dynamical signatures of theQPT show two broad classes of behavior, corresponding to the collapse of eithera Kondo resonance, or antiresonance, as the transition is approached from theFermi liquid phase; the latter behavior being apparent in experimentaldifferential conductance maps. The problem is studied using the numericalrenormalization group method, combined with analytical arguments.



Autor: David E. Logan, Christopher J. Wright, Martin R. Galpin

Fuente: https://arxiv.org/







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