We investigated electron transport through an ultrasmall Si quantum dot. Th
e B dependence of energy levels is dominated by the Zeeman shift, allowing
us to measure the spin difference between two successive ground states dire
ctly. 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 with a large spi
n change DeltaS=3/2, demonstrating the essential features of spin blockade.
Surprisingly, for N>20, the transitions with DeltaS>1/2 do not lead to the
suppression of the corresponding peaks at low temperatures.