A new metallic state in two dimensions

We report the discovery of a new and unexpected kind of metal in two dimensions (2D), which exists in the presence of scattering by local magnetic moments. The experiment was carried out on a 2D electron system in silicon, where the local magnetic moments have been induced by disorder and their number was varied using substrate bias (Vsub). In the new metal, the conductivity decreases as σ(ns,T)=σ(ns,T=0)+A(ns)T2 (ns – carrier density) to a non-zero value as temperature T→0. In three dimensions, this T2 dependence is well known, and results from Kondo scattering by local magnetic moments. In 2D, however, the existence of a metal with dσ/dT>0 is very surprising. As the number of local moments is reduced, the range of temperatures [TTm, we observe the usual 2D metallic behavior with dσ/dT<0.