Electronic Design

Polymer Superconducts At Supercold Temperatures

Twenty years of polymer research have borne fruit for Bell Labs. Researchers at its Murray Hill, N.J., facility, in collaboration with the University of Konstanz in Germany, have transformed plastic material into superconductors, opening new frontiers for organic polymers.

While developers have known how to convert organic polymers to electrical conductors since the early seventies, creating a superconducting poly-mer has seemed far-fetched. Removing electrons from polythiophene and cooling the material to −455°F, though, makes the impossible possible.

The scientists say that polythiophene, which can be a conductor at room temperature and has been used in making optoelectronic components, may be the first of many superconducting plastics. The challenge was overcoming the inherent structural randomness of the polymer—similar to strands of cooked spaghetti—which prevented the electronic interactions necessary for superconductivity.

By making a solution containing the plastic polythiophene and then depositing thin films of it onto an underlying substrate, the polymer molecules stacked up against one another like uncooked spaghetti. Instead of adding chemical impurities to change the material's electrical properties, as is often done, the researchers used a novel technique to inject charge carriers into polythiophene thin film.

As reported in the March 8 issue of Nature, this feat was achieved by using a field-effect transistor (FET) geometry. The film was then cooled to −455°F to observe superconductivity. Although this is extremely cold, scientists are optimistic that they can raise the temperature in the future by altering the polymer's molecular structure.

"With the method we used, many organic materials may potentially be made superconducting now," says Zhenan Bao, a Bell Labs chemist who was involved in the research. Bell Labs scientists plan to study the inter-relationships between semiconducting, superconducting, and molecular electronics with materials such as polythiophene in the coming months.

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