Giant spin thermoelectric effects in all-carbon nanojunctions

We examine the thermospin properties of an all-carbon nanojunction constructed by a graphene nanoflake (GNF) and zigzag-edged graphene nanoribbons (ZGNRs), bridged by the carbon atomic chains. The first-principles calculations show that the phonon thermal conductance is much weaker than the electron thermal conductance at the Fermi level, and even the former is a few percent of the latter in the low-temperature regime. In the meantime, the carbon-based device possesses an excellent spin transport property at the Fermi level due to the appearance of half-metallic property. Furthermore, the single-spin Seebeck coefficient has a larger value at the Fermi level. These facts ultimately result in a significant enhancement of spin thermoelectric figure of merit (FOM) ZST. By controlling the carbon-chain lengths and the temperature, the maximal value of ZST can reach 30. Moreover, we also find that the room temperature ZST displays an odd-even effect with the carbon-chain lengths, and it is always larger than the charge thermoelectric FOM ZCT.