Fig. 3: Fermi-liquid to Dirac-fluid crossover.
From: Observation of giant and tunable thermal diffusivity of a Dirac fluid at room temperature
a–d, Time-zero spatial maps of ∆ITE for low optical power P and high gate voltage ∆U with an np junction (a) and with a pn junction (d); and for high optical power and low gate voltage with an np junction (b), and with a pn junction (c). For larger ratio Te/TF (that is, larger P/∆U) the spatial extent is clearly larger. e,f, Time zero Gaussian widths for spatial scans with one pulse on the junction and the second one scanning across (e) and along (f) the graphene pn junction, as a function of P and ∆U. The strong dependence on Te/TF demonstrates our ability to transition under control into the Dirac-fluid regime with strongly increased thermal diffusivity. g,h, Calculation of the thermal diffusivity following refs. 6,18 with only electron–electron interactions (g) and only long-range Coulomb scattering (h). The contours in g are the calculated time zero spreads \(\sigma _{{{{\mathrm{calc}}}}}^2\) (Methods).
