Continuous and discontinuous metal-insulator transitions

Abstract

In non-crystalline systems a continuous metal-insulator transition of Andersontype is frequently observed when the Fermi energy moves through a mobility edge. In crystalline systems, on the other hand, the activation energy for conduction should change discontinuously at the transition. The aim of this paper is to enquire under what conditions a discontinuous transition can occur in non-crystalline systems. It clearly does not in the impurity band of Si : P when the concentration is varied; it probably does in films of Pb—Ar and is thought to do so in liquids such as metal-ammonia and expanded liquid caesium. For the latter, in contrast with mercury, the critical point is believed to be similar to that in metal-ammonia and to lie between a metallic and non-metallic liquid. The concept due to Landau and Zeldovich (1943) of a fluid with two critical points is applied to these fluids and to electron-hole droplets.