The conductivity of an amorphous sample at low temperatures in a strong magnetic field is calculated. While Mott's and Ono"s theories consider infinite samples, the proposed formalism treats finite ones. It turns out that this is a crucial difference. The model shows a transition between two conductivity behaviors: ln (σ)≈${\mathrm{T}}^{\mathrm{-}1\mathrm{/}3}$ for T${\mathrm{T}}^{\mathrm{-}1\mathrm{/}2}$ for T>T-tilde (the transition temperature T-tilde depends on the magnetic field and on the sample's size). The former one resembles the simple two-dimensional Mott conductivity behavior, while the latter resembles Ono"s theory.

• Received 30 December 1996

DOI:https://doi.org/10.1103/PhysRevB.55.15828