Quantum Dots with Even Number of Electrons: Kondo Effect in a Finite Magnetic Field

We show that the Kondo effect can be induced by an external magnetic field in quantum dots with an even number of electrons. If the Zeeman energy $B$ is close to the single-particle level spacing $\Delta$ in the dot, the scattering of the conduction electrons from the dot is dominated by an anisotropic exchange interaction. A Kondo resonance then occurs despite the fact that $B$ exceeds by far the Kondo temperature $T_K$. As a result, at low temperatures $T\ll T_K$ the differential conductance approaches a unitary limit $G_K\sim e^2/\pi ħ$. A possible experimental realization of this effect is discussed.