SU(4) Fermi Liquid State and Spin Filtering in a Double Quantum Dot System

Abstract

We study a symmetrical double quantum dot (DD) system with strong capacitive interdot coupling using renormalization group methods. The dots are attached to separate leads, and there can be a weak tunneling between them. In the regime where there is a single electron on the DD the low-energy behavior is characterized by an SU(4)-symmetric Fermi liquid theory with entangled spin and charge Kondo correlations and a phase shift pi/4. Application of an external magnetic field gives rise to a large magnetoconductance and a crossover to a purely charge Kondo state in the charge sector with SU(2) symmetry. In a four-lead setup we find perfectly spin-polarized transmission.

Universal scaling of the quantum conductance of an inversion-symmetric interacting model

“…8 with the corresponding values of g obtained from Eq. (27). One can see that the behavior of g given by the NRG algorithm and Eq.…”

“…As pointed out in previous works [27][28][29] , the quantum conductance g can be directly extracted from the NRG spectra. Let us consider an NRG chain of even length N → ∞.…”

“…Let us check that the NRG algorithm and Eq. (27) give us the correct behavior for the conductance g in the noninteracting limit where it is straightforward to solve the scattering problem. One obtains…”

Kondo effect and spin filtering in triangular artificial atoms

“…In this state orbital and spin fluctuations are entirely entangled. As opposed to the usual Kondo state with phase shift π/2, this SU (4) Kondo state is characterized by a phase shift δ = π/4, and is very similar to states proposed recently for artificial molecules (two coupled artificial atoms) [9]. The unusual phase shift could be detected by integrating the TA into an Aharanov-Bohm geometry [10], but could also be inferred from more standard transport measurents.…”

“…The major difference between the artificial molecule system of Ref. [9] and the present triangular arrangement is that in the former case the orbital states of the full system are never truly degenerate because of tunneling between the two sites, while in a perfectly symmetrical TA the Γ 3 states are far closer to degeneracy, split only by a small spin-orbit interaction. Furthermore, the Γ 3 electronic wave functions on the TA strongly overlap with each other, producing a large Hund's rule coupling, and hence a triplet ground state for double occupancy of the four-fold degenerate state.…”