Electron tunneling experiments are used to probe Coulomb correlation effectsin the single-particle density-of-states (DOS) of boron-doped silicon crystalsnear the critical density of the metal-insulator transition (MIT). At lowenergies, a DOS measurement distinguishes between insulating and metallicsamples with densities 10 to 15 % on either side of the MIT. However, at higherenergies the DOS of both insulators and metals show a common behavior,increasing roughly as the square-root of energy. The observed characteristicsof the DOS can be understood using a classical treatment of Coulombinteractions combined with a phenomenological scaling ansatz to describe thelength-scale dependence of the dielectric constant as the MIT is approachedfrom the insulating side.
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