Extended Data Fig. 1: Electrical mobility measurement.
From: Observation of giant and tunable thermal diffusivity of a Dirac fluid at room temperature
Momentum relaxation time from four-probe measurements and corresponding (calculated) heat diffusivity (solid line). Four-probe measurements were performed by applying 1 V to a MΩ series resistor, such that a current of 1 μA flows between the two outer contacts of the device (see inset). We then measure the voltage drop between two lateral contacts of the graphene device. This yields the sheet conductance σ as a function of gate voltage. We then use σ = neμ, in order to extract the mobility µ and use \(\tau _{mr} = \frac{{\mu E_{{{\mathrm{F}}}}}}{{ev_{{{\mathrm{F}}}}^2}}\) to obtain the momentum relaxation time. Here, n is the carrier density, EF is the Fermi energy, vF ≈ 106 m/s is the Fermi velocity, and e is the elementary charge. We measured up to EF = 150 meV, and extrapolated the data to higher Fermi energies. The three symbols indicate the Fermi energy and predicted diffusivity corresponding to the diffusivity measurements in Fig. 2e.
