Spin blockade in many-electron ground state resonances of a quantum dot

We present measurements on spin blockade in a laterally integrated quantum dot. The dot is tuned into the regime of strong Coulomb blockade, confining $\sim 50$ electrons. At certain spin states we find an additional mechanism suppressing electron transport, which we identify as spin blockade at zero bias. We verify this by probing the bias, magnetic field and temperature dependence. Weak violation of this blockade is modelled by detailed calculations of non-linear transport taking into account forbidden spin transitions.