Screening breakdown on the route toward the metal-insulator transition in modulation doped Si/SiGe quantum wells - art. no. 026401

Exploiting the spin resonance of a two-dimensional (2D) electron in SiGe/Si quantum wells, we determine the carrier density dependence of the magnetic susceptibility. Assuming weak interaction, we evaluate the density of stat es at the Fermi level, D (E-F), and the screening wave vector, q(TF) Instea d of the constant values of an ideal 2D system, we observe a gradual decrea se towards the band edge. Calculating the mobility from q(TF) yields good a greement with experimental values justifying the approach. The decrease in D(EF) is explained by potential fluctuations which lead to tail states that make screening less efficient and, in a positive feedback, cause an increa se of the potential fluctuations.