Strong Coulomb drag and broken symmetry in double-layer graphene

By R. Gorbachev, A.K. Geim, M. Katsnelson, K. Novoselov, T. Tudorovskiy, I. V. Grigorieva, Allan H. MacDonald, Kenji Watanabe, Takashi Taniguchi, L. Ponomarenko. Nature Physics, 2012

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Coulomb drag is a frictional coupling between electric currents flowing in spatially separated conducting layers. It is caused by interlayer electron–electron interactions. Previously, only the regime of weak (d≫l) to intermediate (d∼l) coupling could be studied experimentally, where dis the interlayer separation and l is the characteristic distance between charge carriers. Here we use graphene–boron-nitride heterostructures with d down to 1 nm to probe Coulomb drag in the limit d≪l such that the two Dirac liquids effectively nest within the same plane, but can still be tuned and measured independently. The strongly interacting regime reveals many unexpected features. In particular, although drag vanishes because of electron–hole symmetry when either layer is neutral, we often find drag strongest when both layers are neutral. Under this circumstance, drag is positive in zero magnetic field but changes its sign and rapidly grows in strength with field. The drag remains strong at room temperature. The broken electron–hole symmetry is attributed to mutual polarization of closely spaced interacting layers. Two closely spaced two-dimensional systems can remain strongly coupled by electron–electron interactions even though they cannot physically exchange particles. Coulomb drag is a manifestation of this interaction—in which an electric current passed through one layer causes frictional charge flow in the other—now experimentally observed in bilayer graphene

Subfields: Atomic and Molecular Physics, and Optics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/f8d697d783a6ba08cb467eef8361885252bbfe84

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Citations in the corpus

Electronic properties of graphene-based bilayer systems (2015, background): “278,279,280]. The experimental observation of the Coulomb drag in an articial structure of two graphene sheets with a dielectric barrier between them has been reported by R. Gorbachev et al. in Ref. [281]. 68 The crossover temperature T, at which the transition from ordered phase to PM state occurs,”
2D materials and van der Waals heterostructures (2016, methodology): “This method allows for very-high-quality Coulombdrag devices, where two graphene layers, separated galvanically, interact through Coulomb forces between the charge carriers in the two layers (68).”
Strong Light-Matter Interactions in Heterostructures of Atomically Thin Films (2013, background): “It has, for instance, been shown that layering sheets of graphene and hexagonal boron nitride (hBN),molybdenumdisulfide (MoS2), or tungsten disulfide (WS2) allows operation of tunneling transistors (9, 10) and permitted the observation of phenomena such as Coulomb drag (11) and the fractional quantu”