Coulomb drag is a non-invasive tool for probing the interlayer electron-electron interactions in bilayer systems. It is a transport phenomenon where an open circuit voltage (VD) appears in one of the conductors belonging to an electrically isolated conductor pair while passing current (ID) through the opposite conductor, as a result of interlayer momentum and energy transfers mediated by the Coulomb interaction. Coulomb drag has been a direct probe of electronic interactions in diverse class of systems, both Momentum and Energy drag has been observed in bilayer graphene systems. In two-dimensional bilayer heterostructures, correlated charge inhomogeneity breaks the electron-hole symmetry and gives rise to nonzero drag signal at the charge neutrality point. Many theories have been proposed to explain the drag signal with no consensus among them. Coulomb drag measurements in dimensionally mismatched system consisting of a 2D graphene and a 1D InAs nanowire has potential to unravel the drag mechanism. We have attempted to study the Coulomb drag in novel drag systems consisting of a two-dimensional (2D) graphene and a one-dimensional (1D) InAs nanowire (NW)heterostructure exhibiting distinct results from 2D-2D heterostructures. For monolayer graphene (MLG)-NW heterostructures, we observe an unconventional drag resistance peak near the Dirac point due to the correlated interlayer charge puddles. The drag signal decreases monotonically with temperature () and with the carrier density of NW () but increases rapidly with the magnetic field (). These anomalous responses, together with the mismatched thermal conductivities of graphene and NWs, establish the energy drag as the responsible mechanism of Coulomb drag in MLG-NW devices. In contrast, for bilayer graphene (BLG)-NW devices the drag resistance reverses sign across the Dirac point and the magnitude of the drag signal decreases with the carrier density of the NW (), consistent with the momentum drag. Coulomb drag as a non-invasive tool can be employed for diverse class of systems for a direct measurement of electronic interactions. Recent experiments on twisted bilayer graphene heterostructures unravelled a plethora of phases like unconventional superconductivity, correlated insulators arising from unique flat bands of the system where the electronic interactions play the major role. Coulomb drag can also be utilised as a unique probe for investigating and tuning the electronic interactions in those systems.
Richa Mitra, Manas Ranjan Sahu, Kenji Watanabe, Takashi Taniguchi, Hadas Shtrikman, A.K Sood and Anindya Das
Physical Review Letters 124 (11), 116803 (2020)
(Top) positive correlation of charge puddles between the layers. Right side; thermal correlation due to energy drag. (Bottom) SEM picture of InAs nanowire with graphene. Drag resistance as a function drive current and graphene carrier density. Drag signal as a function of temperature.