Comments on D.C. conductivity in amorphous semiconductors

A recent paper in this journal argued that the electrical conductivity arising from thermal hopping between localized states obeys the law in $\text{ln}\text{σ∝ — (T}{}_{\mathrm{<mtext>0</mtext>}}\text{/T)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$, at low temperatures. That result is found to be based on several unjustified assumptions, however, and the correct temperature dependence is $\text{ln}\text{σ∝ — (T}{}_{\mathrm{<mtext>0</mtext>}}\text{/T)}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$, as originally proposed by Mott.