Insulating /metalhc transition

Several studies have indicated thatlinePAni)-emeraldine salt(S) / 2-acrylami-do-2 mthyl -1-propane sulfonic acid (AMPSA) [7,8,9,10] cast id (DCAA) is in the metallic regime toward the insulator-metal transition. The metallic beaviour was attributed to the criterion of finite conductivity when TDO K, the positive slope of the temperature dependence reduced activation energy (i.e W (T) = d [log o(T)]/d [log(T)]),liseddelocalized electronic states at the Fermi level that allow condnction without thermal activation. However, this polymer does not show metalhc behavior over the whole range of temperatures. They exhibit semiconducting (da/dT) > 0) and... 

Both phases exhibit metalhc character at RT with <7rt — 90 and 20-70 2 cm for the H2O- and C4H802-derived materials, respectively. The water pseudoiso-morph remains metallic down to 4.2 K while the C4H8O2 pseudoisomorph shows a rather sharp metal-insulator transition below c. 100 K. In this case the metallic state is restored down to 4.2 K by application of hydrostatic pressures of 15 kbar. 

Depending on the crystal structure of the one-dimensional stacks and on whether a Peierls transition occurs or not (more on this subject wiU be given in Sect. 9.3), the states in the one-dimensional bands are wholly or partiaUy fUled. The CT crystals can therefore be semiconductors or metalHc conductors. If at high temperature metallic conductivity is present and at a lower temperature Tp a Peierls phase transition occurs, the metal becomes a semiconductor at T< Tp, or an insulator. 

The paramagnetism of the conduction electrons, not observable by ESR, can however be detected by a measurement of the magnetic susceptibility. In the region of metalhc conductivity, one observes in the contribution of the conduction electrons a nearly temperature-independent Pauli susceptibility, well known from metals. In those crystals which undergo a Peierls transition and become semiconductors or insulators at low temperatures, the Pauli susceptibility is transformed into a Curie-law behaviour. The susceptibility then increases with further decreasing tern-... 

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