Strong Coulomb drag and broken symmetry in double-layer graphene

Abstract

Spatially separated electron systems remain strongly coupled by electron-electron interactions even when they cannot exchange particles, provided that the layer separation d is comparable to a characteristic distance l between charge carriers within layers. One of the consequences of this remote coupling is a phenomenon called Coulomb drag, in which an electric current passed through one of the layers causes frictional charge flow in the other layer. Previously, only the regime of weak (d>>l) to intermediate (d ~ l) coupling could be studied experimentally. Here we use graphene-BN heterostructures with d down to 1 nm to probe interlayer interactions and Coulomb drag in the limit d<<l where the two Dirac liquids effectively nest within the same plane, but still can be tuned and measured independently. The strongly interacting regime reveals many unpredicted features that are qualitatively different from those observed previously. In particular, although drag vanishes because of electron-hole symmetry when either layer is neutral, we find that drag is at its 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. The two-fluid Dirac system offers a large parameter space for further investigation of strong interlayer interaction phenomena

Gate-Tunable Resonant Tunneling in Double Bilayer Graphene Heterostructures

“…Combining such materials in vertical heterostructures may provide new insight into the electron physics in these materials through Coulomb drag [3], [4] or tunneling [5], [6]. Tunneling between two distinct 2D carrier systems, namely 2D-2D tunneling has been used in GaAs 2D electron [7], [8] and 2D hole systems [9]- [11] as a technique to probe the Fermi surface and quasi-particle lifetime.…”

Hydrodynamics in graphene: Linear-response transport

“…In Sec. V, we apply our theory to double-layer graphene-based systems [16][17][18][19]. Concluding remarks can be found in Sec.…”

“…[9,10] and then extended to double-layer graphene-based structures in Ref. [11], which allowed for a description of the Coulomb drag effect [16][17][18][19] in graphene. An extension of this approach to mesoscopic (finite-size) samples was suggested in Ref.…”

Plasmonic excitations in Coulomb-coupledN-layer graphene structures

“…Substantial efforts have been directed towards the investigation of the linear response of doped graphene 24 and of the charge density excitations [25][26][27][28][29] and of such complex quasiparticles as plasmarons 30,31 and plasmon-phonon complexes 32 . Recently, the experimental realization of graphene double-layer structures coupled only via the Coulomb interaction [33][34][35][36][37][38] has attracted substantial theoretical interest in studying the double-layer plasmon effects [39][40][41][42] and the frictional drag 43 in two spatially separated graphene layers [44][45][46][47][48][49][50][51][52] as powerful tools for probing interaction effects of massless Dirac fermions.…”