Giant Frictional Drag in Double Bilayer Graphene Heterostructures

TL;DR

This paper reports a large, anomalous negative frictional drag in double bilayer graphene separated by hBN, with temperature-dependent behavior suggesting a thermoelectric origin, especially near charge neutrality at very low temperatures.

Contribution

It reveals a giant, negative frictional drag in double bilayer graphene at low temperatures, indicating a thermoelectric mechanism not previously observed in such heterostructures.

Findings

Large negative drag resistivity near charge neutrality

Drag resistivity increases as temperature decreases

Breakdown of layer reciprocity at low temperatures

Abstract

We study the frictional drag between carriers in two bilayer graphene flakes separated by a 2 $-$ 5 nm thick hexagonal boron nitride dielectric. At temperatures ($T$) lower than $\sim$ 10 K, we observe a large anomalous negative drag emerging predominantly near the drag layer charge neutrality. The anomalous drag resistivity increases dramatically with reducing {\it T}, and becomes comparable to the layer resistivity at the lowest {\it T} = 1.5 K. At low $T$ the drag resistivity exhibits a breakdown of layer reciprocity. A comparison of the drag resistivity and the drag layer Peltier coefficient suggests a thermoelectric origin of this anomalous drag.