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 ν 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.
As a first step towards a new measurement of the W boson mass with the LHCb experiment the role of proton structure uncertainties is studied in detail, resulting in interesting new ideas.
In recent months, work from the XPS Facility has contributed to publications on attaching antifreeze proteins to nanoparticles to modulate the formation and growth of ice at sub-zero temperatures, including an article in the Pioneering Inverstigators issue of Polymer Science.
A methodology is developed for chemically modifying DNA nanoflowers so as to increase stability and introduce magnetic properties.