Seebeck Coefficient of a Single van der Waals Junction in Twisted Bilayer Graphene

TL;DR

This paper reveals that the Seebeck coefficient in twisted bilayer graphene is governed by interlayer phonon drag, showing non-monotonic behavior and potential for tunable thermoelectric applications.

Contribution

It demonstrates that interlayer phonon interactions dominate the Seebeck effect in twisted bilayer graphene, differing from traditional tunneling models.

Findings

Seebeck coefficient is affected by out-of-plane phonon modes.

The thermovoltage exhibits non-monotonic temperature and density dependence.

Interlayer phonon drag can be tuned for thermoelectric applications.

Abstract

When two planar atomic membranes are placed within the van der Waals distance, the charge and heat transport across the interface are coupled by the rules of momentum conservation and structural commensurability, leading to outstanding thermoelectric properties. Here we show that an effective "interlayer phonon drag" determines the Seebeck coefficient (S) across the van der Waals gap formed in twisted bilayer graphene (tBLG). The cross-plane thermovoltage, which is non-monotonic in both temperature and density, is generated through scattering of electrons by the out-of-plane layer breathing (ZO'/ZA2) phonon modes and differs dramatically from the expected Landauer-Buttiker formalism in conventional tunnel junctions. The tunability of the cross-plane Seebeck effect in van der Waals junctions may be valuable in creating a new genre of versatile thermoelectric systems with layered solids.