Electron Tunneling Study of Coulomb Correlations across the Metal-Isulator Transition in Si:B

Electron tunneling gives an empirical description of how Coulomb correlations evolve across the metal-insulator transition (MIT) in Si:B. For clearly insulating or metallic samples, the tunneling conductance displays a parabolic or a square-root shape, respectively. Just below the MIT, the conductance shows some metallic features before the samples become truly metallic. Very close to the MIT, the conductance spectra are unusually broad and frequency dependent. We interpret this last feature as a result of long-wavelength screening arising from a divergence of the dielectric constant.