Electron-electron interactions and the metal-insulator transition in heavily doped silicon


  • This article is dedicated to Dieter Vollhardt on the occasion of his 60th birthday.


The metal-insulator (MI) transition in Si:P can be tuned by varying the P concentration or – for barely insulating samples – by application of uniaxial stress S. On-site Coulomb interactions lead to the formation of localized magnetic moments and the Kondo effect on the metallic side, and to a Hubbard splitting of the donor band on the insulating side. Continuous stress tuning allows the observation of finite-temperature dynamic scaling of σ (T,S) and hence a reliable determination of the critical exponent μ of the extrapolated zero-temperature conductivity σ (0) ∼ | S - Sc |μ, i.e., μ = 1, and of the dynamical exponent z = 3. The issue of half-filling vs. away from half-filling of the donor band (i.e., uncompensated vs. compensated semiconductors) is discussed in detail.