Coulomb Drag In Graphene Research Articles

Coulomb drag between two graphene layers at different temperatures

We theoretically study the Coulomb drag in graphene when there is a temperature difference between the layers. Within the degenerate limit for equal layer densities, we find that this can lead to significant deviations from the usual quadratic temperature dependence of the drag resistivity. The exact behavior depends strongly on the phase space available for intraband scattering, and is not symmetrical when the temperatures of the layers are interchanged. In particular, when one layer is at a much higher temperature $T$ than the other, the drag resistivity behaves as $\rho_D\sim T/d^5$, where $d$ is the interlayer separation. The magnitude of the drag in this limit is always larger when the active layer is at the higher temperature.

Effect of quasiparticle excitations and exchange-correlation in Coulomb drag in graphene

Coulomb drag in double layer graphene systems separated by an h-BN interlayer allows probing of the electron-electron interactions in the effective limit of zero layer separation. Although these interactions can be influenced by plasmons, phonons and exchange and correlation effects, these excitations have never been studied altogether, missing the effects of their coupling on the drag physics. Here we study theoretically the effects of these quasiparticles and their coupling, including also the effects of the electronic exchange and correlation, and demonstrate that the drag resistivity can attain a maximum value at room temperature and beyond, where hybridized plasmon-phonon modes contribute significantly. In particular, the hybridization of the plasmons with the hyperbolic phonons of h-BN, confined within the reststrahlen bands, enhance the drag resistivity. This study paves the way for the exploration of novel many-body physics phenomena in systems coupled through emerging 2D hyperbolic materials.

Coulomb Drag Mechanisms in Graphene

Recent measurements revealed an anomalous Coulomb drag in graphene, hinting at new physics at charge neutrality. The anomalous drag is explained by a new mechanism based on energy transport, which involves interlayer energy transfer, coupled to charge flow via lateral heat currents and thermopower. The old and new drag mechanisms are governed by distinct physical effects, resulting in starkly different behavior, in particular for drag magnitude and sign near charge neutrality. The new mechanism explains the giant enhancement of drag near charge neutrality, as well as its sign and anomalous sensitivity to the magnetic field. Under realistic conditions, energy transport dominates in a wide temperature range, giving rise to a universal value of drag which is essentially independent of the electron-electron interaction strength.

Coulomb Drag in Graphene Near the Dirac Point

We study Coulomb drag in graphene near the Dirac point, focusing on the regime of interaction-dominated transport. We establish a novel, graphene-specific mechanism of Coulomb drag based on fast interlayer thermalization, inaccessible by standard perturbative approaches. Using the quantum kinetic equation framework, we derive a hydrodynamic description of transport in double-layer graphene in terms of electric and energy currents. In the clean limit the drag becomes temperature independent. In the presence of disorder the drag coefficient at the Dirac point remains nonzero due to higher-order scattering processes and interlayer disorder correlations. At low temperatures (diffusive regime) these contributions manifest themselves in the peak in the drag coefficient centered at the neutrality point with a magnitude that grows with lowering temperature.

Charges driving under the influence

An investigation of Coulomb drag in graphene integrated into a stacked heterostructure unveils unexpected electron–hole symmetry-breaking in two-dimensional electronic crystals.

Coulomb drag in monolayer and bilayer graphene

We theoretically calculate the interaction-induced frictional Coulomb drag resistivity between two graphene monolayers as well as between two graphene bilayers, which are spatially separated by a distance $d$. We show that the drag resistivity between graphene monolayers can be significantly affected by the intralayer momentum-relaxation mechanism. For energy-independent intralayer scattering, the frictional drag induced by interlayer electron-electron interaction goes asymptotically as ${\ensuremath{\rho}}_{D}\ensuremath{\sim}{T}^{2}/{n}^{4}{d}^{6}$ and ${\ensuremath{\rho}}_{D}\ensuremath{\sim}{T}^{2}/{n}^{2}{d}^{2}$ in the high-density (${k}_{F}d\ensuremath{\gg}1$) and low-density (${k}_{F}d\ensuremath{\ll}1$) limits, respectively. When long-range charge impurity scattering dominates within the layer, the monolayer drag resistivity behaves as ${\ensuremath{\rho}}_{D}\ensuremath{\sim}{T}^{2}/{n}^{3}{d}^{4}$ and ${T}^{2}\mathrm{ln}(\sqrt{n}d)/n$ for ${k}_{F}d\ensuremath{\gg}1$ and ${k}_{F}d\ensuremath{\ll}1$, respectively. The density dependence of the bilayer drag is calculated to be ${\ensuremath{\rho}}_{D}\ensuremath{\propto}{T}^{2}/{n}^{3}$ both in the large and small layer separation limit. In the large layer separation limit, the bilayer drag has a strong $1/{d}^{4}$ dependence on layer separation, whereas this goes to a weak logarithmic dependence in the strong interlayer correlation limit of small layer separation. In addition to obtaining the asymptotic analytical formula for Coulomb drag in graphene, we provide numerical results for arbitrary values of density and layer separation interpolating smoothly between our asymptotic theoretical results.

Theory of Coulomb drag in graphene

We study the Coulomb drag between two single graphene sheets in intrinsic and extrinsic graphene systems with no interlayer tunneling. The general expression for the nonlinear susceptibility appropriate for single-layer graphene systems is derived using the diagrammatic perturbation theory, and the corresponding exact zero-temperature expression is obtained analytically. We find that, despite the existence of a nonzero conductivity in an intrinsic graphene layer, the Coulomb drag between intrinsic graphene layers vanishes at all temperatures. In extrinsic systems, we obtain numerical results and an approximate analytical result for the drag resistivity ${\ensuremath{\rho}}_{\mathrm{D}}$, and find that ${\ensuremath{\rho}}_{\mathrm{D}}$ goes as ${T}^{2}$ at low temperature $T$, as $1∕{d}^{4}$ for large layer separation $d$, and $1∕{n}^{3}$ for high carrier density $n$. We also discuss qualitatively the effect of plasmon-induced enhancement on the Coulomb drag, which should occur at a temperature of the order of or higher than the Fermi temperature.