Possibility of Two - channel Spin 12 Kondo Conductance in a Quantum Dot

PACS. 71.10.Ay – Fermi-liquid theory and other phenomenological models. Abstract. – By combining exact diagonalization with scaling method, we show that it is possible to realize two channel spin 1 2 Kondo (2CK) conductance in a quantum dot at Coulomb Blockade, with an odd number of electrons and with contacts in a pillar configuration, as an applied orthogonal magnetic field B is tuned at an appropriate level crossing. A Quantum Dot (QD) weakly coupled to the contacts and tuned in a valley between two conduction peaks (Coulomb Blockade (CB)), is insulating if its charging energy is larger than the thermal energy [1]. However, when the number of electrons at the dot, N , is odd, below a characteristic temperature scale T K , a strongly correlated state between the dot and the contacts sets in, and the typical Kondo resonance in the conduction electron spectral density builds up at the chemical potential of the contacts µ. The striking result is that the linear conductance increases in the CB valley, when the temperature T is lowered, up to the unitarity limit 2e 2 /h for T = 0 [2, 3]. If N is even, the ground state (GS) of the QD is usually a spin singlet and the ordinary Kondo effect cannot occur. Nevertheless, it has been shown that level crossing between states at different S induced by a magnetic field B orthogonal to the dot can restore the degeneracy required for the Kondo effect to take place [4–6]. The occurrence of Kondo physics in quantum dots was predicted long ago in analogy to magnetic impurities in diluted metal alloys at very low temperatures [7]. A dot at CB acts as a single magnetic impurity, but under controlled experimental conditions. A realistic description of the Kondo effect in alloys has to take into account that the impurity states carry also orbital angular momentum together with spin momentum. Hence, electrons with different orbital momentum can access the impurity and both multi-orbital 1-channel Kondo Effect (1CK) and many-channel Kondo effect (MCK) can take place. Total angular momentum is conserved in the scattering, as it is appropriate for an atomic impurity in an isotropic metal [8]. Similarly to the ordinary 1CK, MCK shows a logarithmic low-temperature raise in the resistivity before the perturbative expansion breaks down (T ∼ T K). However, if the number c EDP Sciences