Critical dopant concentration in polyacetylene and phase diagram from a continuous four-Fermi model

The optimized perturbation theory (OPT) method, at finite temperature and finite chemical potential, is applied to the field theory model for polyacetylene. The critical dopant concentration in trans-polyacetylene is evaluated and compared to available experimental data and to previous calculations. The results obtained within the OPT go beyond the standard mean-field (or large-N) approximation by explicitly including finite N effects. A critical analysis of the possible theoretical prescriptions to implement and interpret these corrections to the mean-field results, given the available data, is given. For the typical temperatures probed in the laboratory, our results show that the critical dopant concentration is only weakly affected by thermal effects