  We present the first findings of the spin transistor effect in the Rashba
gate-controlled ring embedded in the p-type self-assembled silicon quantum well
that is prepared on the n-type Si (100) surface. The coherence and phase
sensitivity of the spin-dependent transport of holes are studied by varying the
value of the external magnetic field and the top gate voltage that are applied
perpendicularly to the plane of the double-slit ring and revealed by the
Aharonov-Bohm (AB) and Aharonov-Casher (AC) conductance oscillations,
respectively. Firstly, the amplitude and phase sensitivity of the 0.7(2e2/h)
feature of the hole quantum conductance staircase revealed by the quantum point
contact inserted in the one of the arms of the double-slit ring are found to
result from the interplay of the spontaneous spin polarization and the Rashba
spin-orbit interaction (SOI). Secondly, the values of the AC conductance
oscillations caused by the Rashba SOI are found to take the fractional form
with both the plateaus and steps as a function of the top gate voltage.
