Fluctuation-induced giant magnetoresistance in charge-neutral graphene

Abstract

The Johnson-Nyquist noise associated with the intrinsic conductivity of the electron liquid, induces fluctuations of the electron density in charge-neutral graphene devices. In the presence of external electric and magnetic fields, the fluctuations of charge density and electric current induce a fluctuating hydrodynamic flow. We show that the resulting advection of charge produces a fluctuation contribution to the macroscopic conductivity of the system, $σ_{\mathrm{fl}}$, and develop a quantitative theory of $σ_{\mathrm{fl}}$. At zero magnetic field, $σ_{\mathrm{fl}}$ diverges logarithmically with the system size and becomes rapidly suppressed at relatively small fields. This results in giant magnetoresistance of the system.

Figures (2)

• Figure 1: Illustration of the fluctuation conductivity mechanism for a graphene Hall-bar device. The Johnson–Nyquist noise, Eq. \ref{['eq:Langevin']}, generates spatial and temporal carrier-density fluctuations $\delta n_{\bm{q},\omega}$, shown by wavy lines. Under an applied electric field $\bm{E}$, this induces inhomogeneous hydrodynamic velocity $\delta\bm{u}_{\bm{q},\omega}$, which is correlated with $\delta n_{\bm{q},\omega}$. The resulting advection of charge produces enhancement of the macroscopic conductivity, Eq. \ref{['eq:DCj']}.
• Figure 2: Magnetic field dependence of the fluctuation-induced conductance of charge neutral graphene $\sigma_{\text{fl}}$ corresponding to the main result of Eq. \ref{['eq:sigma-H']} plotted for different values of the parameter $\alpha$ (denoted by the varicolored pattern) defined in Eq. \ref{['eq:H_T']}.