Spin transitions in a small Si quantum dot

We investigated electron transport through an ultrasmall Si quantum dot. The B dependence of energy levels is dominated by the Zeeman shift, allowing us to measure the spin difference between two successive ground states directly. Combined with the ability to change the number of electrons N in the dot between 0 and 30, we are able to map the spin of the dot as a function of N and B. The dot becomes spontaneously polarized at $N=6\mathrm{}$ with a large spin change $\Delta S=3/2,$ demonstrating the essential features of spin blockade. Surprisingly, for $N>\mathrm{}20,$ the transitions with $\Delta S>\mathrm{}1/2\mathrm{}$ do not lead to the suppression of the corresponding peaks at low temperatures.