Isotope Effect of Thermopower in the TTFCOONH3Ph Single Crystal

The thermopowers of single-crystalline anilinium tetrathiafulvalene-2-carboxylate (TTFCOONH3Ph) and its deuteriated form (TTFCOOND3Ph) have been examined at room temperature, and a significant isotope effect was found: 102 mu V/K for TTFCOONH3Ph, and 48 mu V/K for TTFCOOND3Ph, which amounts to a difference of a factor of around two. The origin of the difference, for example, X-ray crystal structure and doping level, was examined based on chemical and physical characterizations, and it was found that very low ion transport drastically enhances the thermopower of holes, giving rise to the large isotope effect.