Thermoelectrics properties of two-dimensional materials with combination of linear and nonlinear band structures

TL;DR

This study analyzes thermoelectric properties of 2D materials with combined linear and nonlinear bands, revealing that two-band models can outperform three-band models in thermoelectric efficiency.

Contribution

It demonstrates that removing the linear conduction band enhances thermoelectric performance, providing insights into band structure optimization for thermoelectric materials.

Findings

Two-band models show higher ZT than three-band models.

Optimal ZT occurs when nonlinear band intersects Dirac bands near Fermi level.

Combining Dirac and nonlinear bands yields similar TE performance, with band position being critical.

Abstract

We investigate thermoelectric (TE) properties of two-dimensional materials possessing two Dirac bands (a Dirac band) and a nonlinear band within the three-(two-)band model using linearized Boltzmann transport theory and relaxation time approximation. In the three-band model, we find that combinations of Dirac bands with a heavy nonlinear band, either a parabolic or a pudding-mold band, does not give much difference in their TE performance. The apparent difference only occurs in the position of the nonlinear band that leads to the maximum figure of merit ($ZT$). The optimum $ZT$ of the three-band model consisting of a nonlinear band is found when the nonlinear band intersects the Dirac bands near the Fermi level. By removing the linear conduction band, or, in other words, transforming the three-band model to the two-band model, we find better TE performance in the two-band model than in the three-band model, i.e., in terms of higher $ZT$ values