  Transport through a quantum dot (QD) in the Kondo regime shows alternating
regions of high and low conductance when both an external magnetic field and
the gate potential controlling the depth of the QD potential are varied. We
present a theoretical analysis of this chessboard aspect of the
magneto-conductance. An effective Kondo Hamiltonian is obtained by means of a
restriction to the Hilbert space supported by just a few low energy states of N
and N(+/-)1 electrons in the QD. We obtain antiferromagnetic exchange couplings
depending on tunneling amplitudes and correlation effects. When either the
magnetic field or the number of electrons in the QD is varied, Kondo
temperature shows large oscillations due to the successive appearance of ground
states having strong and weak correlation effects alternatively.
