Hall effect at a tunable metal-insulator transition

Using a rotating magnetic field, the Hall effect in three-dimensional amorphous GdₓSi_1-x has been measured in the critical regime of the metal-insulator transition for a constant total magnetic field. The Hall coefficient R₀ is negative, indicating electronlike conductivity, with a magnitude that increases with decreasing conductivity. R₀ diverges at the metal-insulator transition, and displays critical behavior with exponent -1 [R₀~(H-HC)^-1]. This dependence is interpreted as a linear decrease in the density of mobile carriers n~R₀^-1~H-HC, indicative of the dominant influence of interaction effects.