Ballistic thermoelectric properties in double-bend graphene nanoribbons

•The thermal conductances are greatly suppressed by the elastic scattering.•Some gaps for electrons can be opened at antiresonance energies.•Near these antiresonance gaps, an enhanced ZTmaxZTmax can be clearly observed.•This ZTmaxZTmax can be effectively tuned by modulating the structural parameters of double-bend GNRs.

Ballistic thermoelectric properties in double-bend graphene nanoribbons (GNRs) are investigated by using the nonequilibrium Green's function. We find that due to the elastic scattering caused by the interface mismatching, the thermal conductance contributed by phonons is greatly reduced, while ballistic transport behaviors for electrons are dramatically demolished, and even some gaps can be opened at antiresonance energies. Near these antiresonance gaps, the maximum value of ZT   (ZTmaxZTmax) can be observed, much larger than that for straight GNRs. Moreover, this ZTmaxZTmax can be effectively tuned by modulating the length or width of double-bend GNRs.