  Experimental results for sequential transport through a lateral quantum dot
in the regime of spin blockade induced by spin dependent tunneling are compared
with theoretical results obtained by solving a master equation for independent
electrons. Orbital and spin effects in electron tunneling in the presence of a
perpendicular magnetic field are identified and discussed in terms of the
Fock-Darwin spectrum with spin. In the nonlinear regime, a regular pattern of
negative differential conductances is observed. Electrical asymmetries in
tunnel rates and capacitances must be introduced in order to account for the
experimental findings. Fast relaxation of the excited states in the quantum dot
have to be assumed, in order to explain the absence of certain structures in
the transport spectra.
