Disorder induced metal-insulator transition in crystalline Ge1Sb2Te4

Localization of charge carriers in crystalline solids has been the subject of numerous investigations over more than half a century. Materials showing a metal to insulator transition (MIT) without a structural change are therefore of great interest. Concepts based on electron correlation (Mott) or disorder (Anderson) are often invoked to explain such an MIT, but a clear distinction between the two mechanisms is difficult. In this study we report the observation of an MIT in crystalline Ge1Sb2Te4 which is caused by disorder-induced localization in the 3-dimensional solid. A combination of X-ray diffraction experiments as well as optical (FT-IR) and electrical measurements reveals that the observed MIT is an intra-grain effect. The Hall carrier density barely changes during the MIT and is much higher than predicted by the Mott criterion. Therefore, the MIT is not of the Mott type, but driven by disorder.