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Spin entanglement and current cross correlations in nonlinear current through Kondo correlated dot - Rui Sakano

ISSP, the university of Tokyo


salle 208a, aile sud LPS, bât 510

In quantum dots, the Kondo effect in the nonequilibrium steady state beyond the linear response regime has been achieved by applying small bias-voltages, which has been shedding light on a new aspect of the local Fermi liquid[1]. The local Fermi liquid is an extension of Landau’s Fermi liquid theory to the Kondo impurity at low energies[2]. It is essentially accounted for by free quasiparticles and renormalized interactions. In electric currents through quantum dots in the Kondo regime, the renormalized interaction excites pairs of quasiparticles that give rise to backscattering currents with an effective charge of 2e[3-7]. This doubly-charged state enhances fluctuation of the electric current through the quantum dot, which has been observed as enhancement of the shot noise or the Fano factor[8-11]. The shot noise in the Kondo dots has elucidated that interacting quasiparticles form charge pairs in the nonlinear current. A question that remains to be answered is if the spins of the quasiparticle pair are entangled.

We explore spin-entanglement of the quasiparticles of the local Fermi liquid excited in nonlinear current through a quantum dot described by the impurity Anderson model with two degenerate orbitals coupled each other via an exchange interaction. Applying the renormalized perturbation theory, we obtain the precise form of the cumulant generating function and cross-correlations for the currents with spin angled to arbitrary directions, up to third order in the applied bias-voltage. It is found that the exchange interaction gives rise to spin-angle dependency in the cross-correlation between the currents through the two different orbitals, and also brings an intrinsic cross-correlation of currents with three different angular momenta.

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