Localization and its absence: a new metallic state for conducting polymers

Area of Science:

• Solid-state physics
• Condensed matter theory
• Materials science

Background:

• Disorder in one-dimensional systems traditionally precludes long-range transport.
• Recent theoretical models challenge this established view.
• Understanding transport in disordered materials is crucial for electronic applications.

Purpose of the Study:

• To investigate the validity of the random dimer model in explaining long-range transport in one dimension.
• To explore the applicability of this model to the insulator-metal transition in conducting polymers.
• To analyze the presence of conducting states in specific polymer systems.

Main Methods:

• Introduction and analysis of the random dimer model.
• Assignment of random site energies to pairs of lattice sites in a linear chain.
• Application of calculations to polyaniline and polyparaphenylene.

Main Results:

• The random dimer model predicts conducting states that allow for near-ballistic particle transport.
• For polyaniline, these conducting states align with the Fermi level in the metallic regime.
• A similar analysis on polyparaphenylene shows conducting states near the band edge.

Conclusions:

• Disorder does not necessarily prevent long-range transport in one-dimensional systems.
• The random dimer model provides a viable framework for understanding the insulator-metal transition in conducting polymers.
• The model's implications extend to other polymers like heavily doped polyacetylene.