Possible influence of the Fermi level position inside the conduction band of high-T c oxides on the temperature dependence of their resistivity

Abstract

The systematic variation of the temperature dependence of the second temperature derivative of the electrical resistivity d 2ϱ dT 2 is reproduced by model calculations, assuming the existence of a narrow conduction band in the vicinity of the Fermi level E F. The analysis of the characteristic features on the d 2ϱ/d T 2 vs. T curve makes it possible to determine both the half-band width T 2=( ϵ 2- ϵ 1)/2 K B , where ϵ 1, ϵ 2 are the band edges, and the Fermi level position with respect to the middle of the band T 1=[ 1 2 (ϵ 1+ϵ 2)-E F]/K B . It is shown that d 2 ϱ/ dT 2 is negative in this model at certain temperatures below T 2 if the condition 0.563 T 2<| T 1|< T 2 is fulfilled, and positive at all temperatures if | T 1| is outside this interval, while dϱ/ dT>0 in both cases. This fact may be responsible for the complex behaviour of the ϱ( T) dependence caused by the change of composition during the metal-insulator transition in high- T c oxides.