BALLISTIC ELECTRON-TRANSPORT THROUGH A QUANTUM POINT-CONTACT DEFINED IN A SI/SI0.7GE0.3 HETEROSTRUCTURE

We have studied the low-temperature (T = 25 mK) ballistic transport of electrons in a split-gate device fabricated from a Si/Si-0.7/Ge-0.3 heterostructure. In the absence of a magnetic field the conductance is quantized in units of i x 4e(2)/h as the gate voltage is tuned where i is the number of occupied subbands. In this system, both the spin and the valley degeneracies have to be taken into account. These can be lifted by applying a perpendicular magnetic field. Magnetic depopulation of the one-dimensional subbands is observed and can be simulated using a simple square well potential model.