One-dimensionality of thermoelectric properties of semiconducting nanomaterials

Thermoelectric conversion, which is the generation of electricity from waste heat, can play an important role in renewable energy use. Lowering the dimensionality of semiconductor thermoelectric materials is a promising approach for improving thermoelectric performance, and ultimately one-dimensional (1D) semiconductor materials have the potential to exhibit maximized performance because of the presence of a 1D electronic structure, such as the van Hove singularity (vHs) in the density of states. However, experimentally verifying the effect of the 1D nature on the thermoelectric performance in semiconductor nanomaterials has been difficult because we cannot observe any traces of the 1D electronic structure in terms of conventional thermoelectric parameters, such as the Seebeck coefficient or power factor. Here, we show that a thermoelectric parameter, the thermoelectrical conductivity (${L}_{12}$), is strongly correlated with the electronic structure and exhibits a unique 1D trace with single-walled carbon nanotubes (SWCNTs). We experimentally clarify that the ${L}_{12}$ of high-purity semiconducting SWCNTs has a peak structure with a chemical potential in the vicinity of the vHs. For comparison, the ${L}_{12}$ of monolayer molybdenum disulfides and graphene, which are chosen as 2D models, shows a different behavior, simply exhibiting constant values. Furthermore, we find that theoretical calculations support these ${L}_{12}$ behaviors, which are consistent with the expected behaviors of 1D and 2D electronic structures. Our results demonstrate that ${L}_{12}$ is a very good parameter for evaluating the traces of dimensionalities, thereby advancing the elucidation of the fundamental thermoelectric properties necessary for the development of low-dimensional materials.