Negative Coulomb Drag in Double Bilayer Graphene

TL;DR

This study measures Coulomb drag in double bilayer graphene, revealing a novel negative drag response at low temperatures and densities, which can be tuned and aligns with momentum drag predictions, advancing understanding of strongly correlated bilayer systems.

Contribution

It reports the first observation of negative Coulomb drag in double bilayer graphene and demonstrates control over this response through device geometry, highlighting new avenues for exploring correlated phases.

Findings

Observation of negative Coulomb drag at low temperatures.

Negative drag can be suppressed by device aspect ratio.

Results align with momentum drag predictions for double BLG.

Abstract

Coulomb drag between parallel quantum wells provides a uniquely sensitive measurement of electron correlations since the drag response depends on interactions only. Recently it has been demonstrated that a new regime of strong interactions can be accessed for devices consisting of two monlolayer graphene (MLG) crystals, separated by few layer hexagonal boron-nitride. Here we report measurement of Coulomb drag in a double bilayer graphene (BLG) stucture, where the interaction potential is anticipated to be yet further enhanced compared to MLG. At low temperatures and intermediate densities a new drag response with inverse sign is observed, distinct from the momentum and energy drag mechanisms previously reported in double MLG. We demonstrate that by varying the device aspect ratio the negative drag component can be suppressed and a response showing excellent agreement with the density and temperature dependance predicted for momentum drag in double BLG is found. Our results pave the way for pursuit of emergent phases in strongly interacting bilayers, such as the exciton condensate.