"Pudding mold" band drives large thermopower in NaxCoO2

In the present study, we pin down the origin of the coexistence of the large thermopower and the low resistivity in Na x CoO 2 . It is revealed that not just the density of states (DOS), the effective mass, nor the band width, but the peculiar shape of the a 1 g band referred to as the “pudding mold” type, which consists of a dispersive portion and a somewhat flat portion, is playing an important role in this phenomenon. The present study provides a new guiding principle for designing good thermoelectric materials.

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