Nonmonotonic temperature-dependent resistance in low density 2D hole gases

The low temperature longitudinal resistance-per-square R-xx(T) in ungated G aAs/AlxGa1-xAs quantum wells of high peak hole mobility 1.7 x 10(6) cm(2) V -1 s(-1) is metallic for 2D hole density p as low as 3.8 x 10(9) cm(-2). Th e electronic contribution to the resistance, R-el(T), is a nonmonotonic fun ction of T, exhibiting thermal activation, R-el(T) proportional to exp(-E-a /kT), for kT much less than E-F and a heretofore unnoted decay R-el(T) prop ortional to 1/T for kT > E-F. The form of R-el(T) is independent of density , indicating a fundamental relationship between the low- and high-T scatter ing mechanisms in the metallic state.