Extended Data Fig. 3: Temperature difference of the absorption spectra, \({{\boldsymbol{A}}}_{{{\boldsymbol{V}}}_{{\bf{G}}},{{\boldsymbol{T}}}_{{\bf{e}}}}\,-{{\boldsymbol{A}}}_{{{\boldsymbol{V}}}_{{\bf{G}}},{{\boldsymbol{T}}}_{{\bf{0}}}}\), obtained by the double-modulation measurement.
From: Observation of hydrodynamic plasmons and energy waves in graphene

The absorption shows a symmetric profile with respect to VG = −0.1 V, the back-gate voltage associated with the charge-neutrality point.