Very High Thermoelectric Power Factor Near Magic Angle in Twisted Bilayer Graphene

TL;DR

This study demonstrates that twisted bilayer graphene exhibits exceptionally high thermoelectric power factors near the magic angle, with tunable properties driven by electronic structure, making it promising for energy and thermal applications.

Contribution

It provides the first detailed theoretical analysis linking twist angle, electronic structure, and thermoelectric performance in TBG, highlighting the peak power factor near the magic angle.

Findings

Room-temperature power factor reaches 40 mW/mK^2 in TBG.

Peak power factor occurs near the magic angle of 1.3°.

Thermoelectric performance improves at lower temperatures.

Abstract

Recent research on twisted bilayer graphene (TBG) uncovered that its twist-angle-dependent electronic structure leads to a host of unique properties, such as superconductivity, correlated insulating states, and magnetism. The flat bands that emerge at low twist angles in TBG result in sharp features in the electronic density of states (DOS), affecting transport. Here we show that they lead to superior and tuneable thermoelectric (TE) performance. Combining an iterative Boltzmann transport equation solver and electronic structure from an exact continuum model, we calculate thermoelectric transport properties of TBG at different twist angles, carrier densities, and temperatures. Our simulations show the room-temperature TE power factor (PF) in TBG reaches 40 mWm$^{-1}$K$^{-2}$, significantly higher than single-layer graphene (SLG) and among the highest reported to date. The peak PF is observed near the magic angle, at a twist angle of $\approx$1.3$^\circ$, and near complete band filling. We elucidate that its dependence is driven by the band gap between lowest and second subband, which improves Seebeck but decreases with twist angle, and Fermi velocity, which dictates conductivity and rises with twist angle. We observed a further increase in the PF of TBG with decreasing temperature. The strong TE performance, along with the ability to fine-tune transport using twist angle, makes TBG an interesting candidate for future research and applications in energy conversion and thermal sensing and management.