  The fundamental properties of valleys are recently attracting growing
attention due to electrons in new and topical materials possessing this
degree-of-freedom and recent proposals for val-leytronics devices. In silicon
MOSFETs, the interest has a longer history since the valley degree of freedom
had been identified as a key parameter in the observation of the controversial
"metallic behaviour" in two dimensions. However, while it has been recently
demonstrated that lifting valley degeneracy can destroy the metallic behaviour,
little is known about the role of intervalley scattering. Here, we show that
the metallic behaviour can be observed in the presence of strong interval-ley
scattering in silicon on insulator (SOI) quantum wells. Analysis of the
conductivity in terms of quantum corrections reveals that interactions are much
stronger in SOI than in conventional MOSFETs, leading to the metallic behaviour
despite the strong intervalley scattering. The prospect of manipulating the
valley degree of freedom in materials like AlAs, 1 silicon 2--4 graphene,
