Coulomb drag driven electron-hole bifluidity in doped graphene

Abstract

Motivated by the notion that a preponderance of Coulomb interactions might lead to hydrodynamics, we carry out an ab initio calculation of the charge carrier transport properties of the electron-hole plasma of doped graphene. We include both the phonon and Coulomb interactions within a momentum and band resolved Boltzmann transport formalism. We find that, under suitable conditions, the strong Coulomb drag effect induces effects like negative conductivity and joint electron-hole hydrodynamics (bifluidity) in the plasma. We also identify the exclusive electron or hole hydrodynamics. We find that there is a strong violation of the Wiedemann-Franz law in the low doped regimes. Our work elucidates the roles of the microscopic scattering mechanisms that drive these hydrodynamic phenomena.

Figures (4)

• Figure 1: Resistivity vs. charge carrier concentration at various temperatures. Positive (negative) sector of the horizontal axis corresponds to majority electron (hole) concentration. Solid green line gives the 300 K measurements from Ref. ponomarenko2024extreme (data obtained from the primary author via private communication and converted to resistivity units). Calculated values are presented in disks for three temperatures: 200 K (blue), 300 K (green), and 400 K (red). Solid (empty) symbols correspond to the theory that includes (excludes) the Coulomb interactions.
• Figure 2: $200$ K spectral conductivity from the valence and conduction bands for hole doped cases. Thick (thin) lines are for a majority hole concentration of $1.3\times10^{12}$ ($2\times10^{11}$) cm$^{-2}$. Solid (dashed) lines denote the theory including (excluding) the Coulomb interactions. The Dirac point is set at zero energy. The contribution from the conduction band (positive energy) is displayed with a factor $10$ enlargement.
• Figure 3: Panels a, b, c: Normalized deviation function $\Delta/\beta$ vs. magnitude of electron wavevector, measured from K point and along the (K-$k_x$)--K--(K+$k_x$) direction of the Brillouin zone. Panel d: Gradient $\partial_{\mathbf{k}}\Delta$ near the $\mathbf{K}$-point for the valence and conduction band. In all plot, lines represent the valence band and disks represent the conduction band. Solid lines and symbols are for the Coulomb enabled theory, whereas dashed lines and empty symbols are for the Coulomb-free theory.
• Figure 4: Lorentz number vs. carrier concentration. Blue, green, and red symbols are for $200$, $300$, and $400$ K, respectively. Solid (broken) lines correspond to the theory including (excluding) the Coulomb interaction. The dashed horizontal line gives the universal Lorentz number ($2.44 \times 10^{-8} \text{ V}^2 \text{ K}^{-2}$) according to the Wiedemann-Franz law.