We have fabricated a high mobility device, composed of a monolayer graphene flake sandwiched between two sheets of hexagonal boron nitride. Conductance fluctuations as functions of a back gate voltage and magnetic field were obtained to check for ergodicity. Non-linear dynamics concepts were used to study the nature of these fluctuations. The distribution of eigenvalues was estimated from the conductance fluctuations with Gaussian kernels and it indicates that the carrier motion is chaotic at low temperatures. We argue that a two-phase dynamical fluid model best describes the transport in this system and can be used to explain the violation of the so-called ergodic hypothesis found in graphene.
A flake of monolayer graphene was sandwiched between boron nitride sheets. Temperature dependent Shubnikov-de Haas measurements were performed to access how this technique influences the electronic properties of the graphene sample. The maximum mobility found in this configuration was approximately 10 cm Vs . From the phase of the oscillations a Berry phase β of 1/2 was obtained indicating the presence of Dirac fermions. We obtained Fermi velocities around [Formula: see text] m s which imply hopping energies close to 2.5 eV. Furthermore, the carrier lifetime is typically higher than that found in graphene supported by SiO, reaching values higher than 700 fs.
We investigate the energy relaxation of hot carriers in a CVD-grown graphene device with a top h-BN layer by driving the devices into the nonequilibrium regime. By using the magnetic field dependent conductance fluctuations of our graphene device as a self-thermometer, we can determine the effective carrier temperature e at various driving currents while keeping the lattice temperature L fixed. Interestingly, it is found that e is proportional to I, indicating little electron-phonon scattering in our device. Furthermore the average rate of energy loss per carrier e is proportional to ( e 2 − L 2 ), suggesting the heat diffusion rather than acoustic phonon processes in our system. The long energy relaxation times due to the weak electron-phonon coupling in CVD graphene capped with h-BN layer as well as in exfoliated multilayer graphene can find applications in hot carrier graphene-based devices.
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