Novel metallic behavior in two dimensions

Experiments on a sufficiently disordered two-dimensional (2D) electron syst em in silicon reveal a new and unexpected kind of metallic behavior, where the conductivity decreases as sigma (n(s),T)= sigma (n(s),T = 0) + A(n(s))T -2 (where n(s) is carrier density) to a nonzero value as temperature T --> 0. In 2D, the existence of a metal with d sigma /dT > 0 is very surprising. In addition, a novel type of a metal-insulator transition obtains, which i s unlike any known quantum phase transition in 2D.