It has been discovered that the disordered material ${\mathrm{Ge}}_{1-x}{\mathrm{Au}}_x$ displays an unusual type of metal-insulator transition as the composition $x$ is varied. The onset of conductivity, as extrapolated to $T=0\mathrm{}$ K, is continuous, and thus the system has no "minimum metallic conductivity."

• Received 8 September 1980

DOI:https://doi.org/10.1103/PhysRevLett.46.46