Conductance and valley splitting in etched Si/SiGe one-dimensional nanostructures

The conductance of strongly confined one-dimensional constrictions fabricated from Si/SiGe two-dimensional electron gases is investigated. Conductance measurements reveal conductance quantization in units of G(0)=2e(2)/h rather than 2G(0)=4e(2)/h, as expected in the presence of valley and spin degeneracy. Furthermore, at temperatures below T=400 mK, small steps and peaklike features, superimposed to the conductance plateaus, become visible. The conductance in the presence of parallel and perpendicular magnetic field shows that significant valley splitting is present even at zero magnetic field. The enhanced valley splitting observed in our etched devices is related to the strong in-plane confinement.