Kondo ground state in a quantum dot with an even number of electrons

Abstract

Kondo conduction has been observed in a quantum dot with an even number of electrons at the Triplet-Singlet degeneracy point produced by applying a small magnetic field $B$ orthogonal to the dot plane. At a much larger field $B\sim B_{\ast }$, orbital effects induce the reversed transition from the Singlet to the Triplet state. We study the newly proposed Kondo behavior at this point. Here the Zeeman spin splitting cannot be neglected, what changes the nature of the Kondo coupling. On grounds of exact diagonalization results in a dot with cylindrical symmetry, we show that, at odds with what happens at the other crossing point, close to $B_{\ast }$, orbital and spin degrees of freedom are ``locked together'', so that the Kondo coupling involves a fictitious spin 1/2 only, which is fully compensated by conduction electrons under suitable conditions. In this sense, spin at the dot is fractionalized. We derive the scaling equation of the system by means of a nonperturbative variational approach. The approach is extended to the $B\ne B_{\ast }$-case and the residual magnetization on the dot is discussed.

13 pages, 4 .eps figures

References in corpus (7)

• Kondo effect in an integer-spin quantum dot
• Direct Coulomb and Exchange Interaction in Artificial Atoms
• Enhancement of Kondo effect in quantum dots with an even number of electrons
• Quantum dots with even number of electrons: Kondo effect in a finite magnetic field
• Conduction through a quantum dot near a singlet-triplet transition
• Spin fractionalization of an even number of electrons in a Quantum dot
• Sequential magnetotunneling in a vertical Quantum Dot tuned at the crossing to higher spin states

Cited by in corpus (13)

• Double quantum dot as a spin rotator
• Non-equilibrium Kondo effect in asymmetrically coupled quantum dot
• Dynamical symmetries in Kondo tunneling through complex quantum dots
• Kondo effect in systems with dynamical symmetries
• Resonance Kondo Tunneling through a Double Quantum Dot at Finite Bias
• Coherence and Coulomb blockade in single electron devices: a unified treatment of interaction effects
• Kondo effect and singlet-triplet splitting in coupled quantum dots in a magnetic field
• Josephson versus Kondo coupling in a quantum dot connected to two superconductors
• Decoherence and Dephasing in Kondo Tunneling through Double Quantum Dots
• Possibility of two-channel orbital Kondo "spin" 1/2 conductance in a quantum dot
• Linear Kondo conductance in a quantum dot
• Selective tuning of spin-orbital Kondo contributions in parallel-coupled quantum dots
• Hamiltonian theory of the strongly-coupled limit of the Kondo problem in the overscreened case