The change in the electrical resistance of a material with magnetic field ― its magnetoresistance ― lies at the heart of many applications, from storing information in a computer to measuring the speed of a car. The resistance of two materials in particular, silver selenide and silver telluride, can be made to increase linearly as the applied magnetic field increases, up to field values at least one million times that of the Earth's magnetic field. This linear response over such a large range makes these semiconductor materials attractive as magnetic-field sensors, although their performance is unusual in terms of basic physics. Parish and Littlewood have tackled the question, as they report on page 162 of this issue, using a combination of fundamental theory and computer simulations. They show that it is not material perfection, but macroscopic disorder and inhomogeneity, that are the essential ingredients for such a remarkable magnetoresistive response.
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