Physics Department News

The first observation of spin dynamics in the Germanium Tin semiconductor can potentially offer a very rich spin physics, whose fundamental understanding is however still absent.

[Cu(pyrimidine)(H2O)4]SiF6.H2O is an unusual S = 1/2 chiral chain with a spin gap that grows linearly with applied magnetic field and a rich excitation spectrum of soliton and breather modes.

A facility that allows scientists to use x-rays to examine materials for purposes as diverse as reducing corrosion on metal artefacts to re-growing teeth from stem cells is set for a multi-million pound upgrade.

The Universities of Warwick and Liverpool have been awarded a further £7.2million to upgrade and operate the XMaS (X-ray Materials Science) beamline, which is a National Research Facility. The facility has received new funding from the Department of Business, Innovation and Skills through the Engineering and Physical Sciences Research Council (EPSRC) to further studies into the atomic and microscopic structures of materials and their properties under different conditions at length scales of ten thousand times smaller than the thickness of a human hair.

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.