Double thermoelectric power factor of a 2D electron system

Two-dimensional electron systems have attracted attention as thermoelectric materials, which can directly convert waste heat into electricity. It has been theoretically predicted that thermoelectric power factor can be largely enhanced when the two-dimensional electron layer is far narrower than the de Broglie wavelength. Although many studies have been made, the effectiveness has not been experimentally clarified thus far. Here we experimentally clarify that an enhanced two-dimensionality is efficient to enhance thermoelectric power factor. We fabricated superlattices of [N unit cell SrTi_1-x Nb _x O₃|11 unit cell SrTiO₃]₁₀ - there are two different de Broglie wavelength in the SrTi_1-x Nb _x O₃ system. The maximum power factor of the superlattice composed of the longer de Broglie wavelength SrTi_1-x Nb _x O₃ exceeded 5 mW m^-1 K^-2, which doubles the value of optimized bulk SrTi_1-x Nb _x O₃. The present approach - use of longer de Broglie wavelength - is epoch-making and is fruitful to design good thermoelectric materials showing high power factor.