No abstract

Using electrical transport experiments and shot noise thermometry, we find strong evidence that "supercollision" scattering processes by flexural modes are the dominant electron-phonon energy transfer mechanism in high-quality, suspended graphene around room temperature. The power law dependence of the electron-phonon coupling changes from cubic to quintic with temperature. The change of the temperature exponent by two is reflected in the quadratic dependence on chemical potential, which is an inherent feature of two-phonon quantum processes.

We have investigated electrical transport and shot noise in graphene field effect devices. In large width over length ratio W/L graphene strips, we have measured shot noise at low frequency (f=600–850 MHz) in the temperature range of 4.2–30 K. We observe a minimum conductivity of 4e2πh and a finite and gate dependent Fano factor reaching the universal value of 13 at the Dirac point, i.e. where the density of states vanishes. These findings are in good agreement with the theory describing that transport at the Dirac point should occur via evanescent waves in perfect graphene samples with large W/L. Moreover, we show and discuss how disorder and non-parallel leads affect both conductivity and shot noise

We have investigated shot noise and conduction of graphene field effect nanoribbon devices at low temperature. By analyzing the exponential I − V characteristics of our devices in the transport gap region, we found out that transport follows variable range hopping laws at intermediate bias voltages 1 < V bias < 12 mV. In parallel, we observe a strong shot noise suppression leading to very low Fano factors. The strong suppression of shot noise is consistent with inelastic hopping, in crossover from one-to two-dimensional regime, indicating that the localization length l loc < W in our nanoribbons.

We have studied electronic conductivity and shot noise of bilayer graphene (BLG) sheets at high bias voltages and low bath temperature T 0 = 4.2 K. As a function of bias, we find initially an increase of the differential conductivity, which we attribute to self-heating. At higher bias, the conductivity saturates and even decreases due to backscattering from optical phonons. The electron-phonon interactions are also responsible for the decay of the Fano factor at bias voltages V > 0.1 V. The high bias electronic temperature has been calculated from shot-noise measurements, and it goes up to ∼1200 K at V = 0.75 V. Using the theoretical temperature dependence of BLG conductivity, we extract an effective electron-optical phonon scattering time τ e-op . In a 230-nm-long BLG sample of mobility μ = 3600 cm 2 V −1 s −1 , we find that τ e-op decreases with increasing voltage and is close to the charged impurity scattering time τ imp = 60 fs at V = 0.6 V.