Thermoelectric properties of two-dimensional (2D) Dirac materials are calculated within linearized Boltzmann transport theory and relaxation time approximation. We find that the gapless 2D Dirac material exhibits poorer thermoelectric performance than the gapped one. This fact arises due to cancelation effect from electron-hole contributions to the transport quantities. Opening the band gap lifts this cancellation effect. Furthermore, there exists an optimal band gap for maximizing figure of merit (ZT ) in the gapped 2D Dirac material. The optimal band gap ranges from 6kBT to 18kBT , where kB is the Boltzmann constant and T is the operating temperature in kelvin. This result indicates the importance of having narrow gaps to achieve the best thermoelectrics in 2D systems. Larger maximum ZT s can also be obtained by suppressing the lattice thermal conductivity. In the most ideal case where the lattice thermal conductivity is very small, the maximum ZT in the gapped 2D Dirac material can be many times ZT of commercial thermoelectric materials. arXiv:1901.03999v2 [cond-mat.mes-hall]

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We performed Boltzmann transport calculation to obtain the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and thermoelectric figure of merit (ZT) for Dirac systems. We found an enhancement of ZT due to the gap opening. When the phonon thermal conductivity is small enough, the optimum ZT in gapped Dirac system can be larger than 1, which is preferable for thermoelectric applications.

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