Effect of screening on Seebeck coefficient in bilayer graphene/AlGaAs electron gas

TL;DR

This study investigates how temperature-dependent screening influences the phonondrag-induced Seebeck coefficient in a bilayer graphene/AlGaAs system below 50 K, revealing strong dependence on carrier density and layer separation.

Contribution

It provides new insights into the screening effects on thermoelectric properties in bilayer graphene systems at low temperatures, highlighting the role of layer separation and carrier density.

Findings

Screening reduces the Seebeck coefficient at low temperatures.

Double-layer screening increases with layer separation.

Screening functions are affected by carrier density and quantum well width.

Abstract

The knowledge of Seebeck coefficient is a key factor in optimization of thermoelectric materials and finding right applications for it. A high sensitivity to structural change makes thermopower measurements an excellent technique for the study on the charge transport properties of a given material. The phonondrag term dominates at low temperature in the Seebeck coefficient This study examines the temperaturedependent screening effect on the phonondraginduced Seebeck coefficient S^g in a bilayer graphene- BLG-AlGaAs-quasi-twodimensional electron gas (q2DEG) system at the temperature below 50 K. The BLG layer interacts with both deformation potential acoustic phonons and stronger piezoelectric field acoustic phonons from AlGaAs/GaAs. We compare the electronphonon interactions in BLG with and without screening by q2DEG. The screening effect reduces particularly at low temperatures and shows a strong dependence on the carrier density in the BLG layer. The doublelayer screening function increases with layer separation d paralleling the monolayer screening at large d. Additionally varying the GaAs quantum well width reveals that increases with width less than 100 \AA under doublelayer screening but remains unchanged beyond this threshold while monolayer screening decreases as the width increases. Both screening functions enhance when the BLG carrier density is lower than that of q2DEG though the magnitude difference between them is minimal