Experimental Prerequisites for a Model of

A model of charge transport that is able to describe the temperature dependence of the electrical dc conductivity c (T) of freshly-prepared samples between 400 mK and 300 K has to be compatible with the following experimental results  

1) The conductivity increases monotonically with increasing temperature in this entire temperature range. 

2) The slope dor/dT (see fig. 5a) has a finite value for the limit of low temperatures (T- 0), while d2or(T)/dT2 is zero, i.e. we find an almost linear temperature dependence for temperatures between 400 mK and 3000 mK  

3) This means in particular that for T- 0, c(T) approaches a finite value Cq, which is about 20 % of the room temperature value. 

4) For the limit of high temperatures, a(T) asymptotically approaches a saturation value Coo, which for most of the samples investigated has values between 30 000 S/cm and 130 000 S/cm. The conductivity a T) has both an upper boundary (otoo) and a lower boundary (0 0) / Cfw/ o between 2.8 and 4.6. 

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