Prediction of Ferromagnetic Correlations in Coupled Double-Level Quantum Dots

Numerical results are presented for transport properties of two coupled double-level quantum dots. The results strongly suggest that under appropriate circumstances the dots can develop a novel ferromagnetic (FM) correlation at quarter-filling (one electron per dot). In the strong coupling regime (Coulomb repulsion larger than electron hopping) and with the inter-dot tunneling larger than the tunneling to the leads, an S=1 Kondo resonance develops in the density of states, leading to a peak in the conductance. A qualitative 'phase diagram', incorporating the new FM phase, is presented. It is also shown that the conditions necessary for the FM regime are less restrictive than naively believed, leading to its possible experimental observation in real quantum dots.