title: Negative Coulomb Drag in Double Bilayer Graphene.
abstract: We report on an experimental measurement of Coulomb drag in a double quantum well structure consisting of bilayer-bilayer graphene, separated by few layer hexagonal boron nitride. At low temperatures and intermediate densities, a novel negative drag response with an inverse sign is observed, distinct from the momentum and energy drag mechanisms previously reported in double monolayer graphene. By varying the device aspect ratio, the negative drag component is suppressed and a response consistent with pure momentum drag is recovered. In the momentum drag dominated regime, excellent quantitative agreement with the density and temperature dependence predicted for double bilayer graphene is found.
authors: Department of Physics, Columbia University, New York, New York 10027, USA.
authors: J I A
authors: JI
authors: Li
authors: National Institute for Materials Science, 1-1 Namiki, Tsukuba, Japan.
authors: T
authors: T
authors: Taniguchi
authors: National Institute for Materials Science, 1-1 Namiki, Tsukuba, Japan.
authors: K
authors: K
authors: Watanabe
authors: Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA.
authors: J
authors: J
authors: Hone
authors: Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors: A
authors: A
authors: Levchenko
authors: Department of Physics, Columbia University, New York, New York 10027, USA.
authors: C R
authors: CR
authors: Dean