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Abstract |
The Anderson metal-insulator transition (MIT) is central to our
understanding of the quantum mechanical nature of disordered materials.
Despite extensive efforts by theory and experiment, there is still no
agreement on the value of the critical exponent describing the
universality of the transition—the so-called “exponent puzzle.” In this
Rapid Communication, going beyond the standard Anderson model, we
employ ab initio methods to study the MIT in a realistic model of a
doped semiconductor. We use linear-scaling density functional theory to
simulate prototypes of sulfur-doped silicon (Si:S). From these we build
larger tight-binding models close to the critical concentration of the
MIT. When the dopant concentration is increased, an impurity band forms
and eventually delocalizes. We characterize the MIT via multifractal
finite-size scaling, obtaining the phase diagram and estimates of ν.
Our results suggest an explanation of the long-standing exponent
puzzle, which we link to the hybridization of conduction and impurity
bands. |
