Bipolar thermoelectric effects in semiconducting carbon nanotubes: Description in terms of one-dimensional Dirac electrons

TL;DR

This paper models thermoelectric effects in semiconducting carbon nanotubes using 1D Dirac electrons, explaining experimental bipolar Seebeck effects and their temperature dependence.

Contribution

It introduces a theoretical scheme based on Dirac electrons to describe thermoelectric responses, including impurity scattering and in-gap states, in semiconducting SWCNTs.

Findings

Explains bipolar thermoelectric effects observed experimentally.

Clarifies temperature dependence of the Seebeck coefficient at low temperatures.

Provides a theoretical framework for thermoelectric responses in 1D Dirac electron systems.

Abstract

The thermoelectric effects in semiconducting single-walled carbon nanotubes (SWCNTs) are investigated based on the linear response theory combined with the thermal Green's function method. It is shown that the electronic states near the lowest conduction band minimum and the highest valence band maximum can be effectively described in terms of one-dimensional (1D) Dirac electrons to which a theoretical scheme is developed to describe the thermoelectric responses making it possible to study the effects of inter-band impurity scattering and in-gap states. Using the proposed scheme, the bipolar thermoelectric effects (i.e., the sign inversion of the Seebeck coefficient) in semiconducting SWCNTs observed in recent experiments are explained. Moreover, the temperature dependence of the Seebeck coefficient of semiconducting SWCNTs at low temperature is clarified.