Testing the Tomographic Fermi Liquid Hypothesis with High-Order Cyclotron Resonance

The tomographic Fermi liquid (TFL) hypothesis posits starkly different relaxation times for odd and even angular harmonics of electron distribution function in two-dimensional systems, but its experimental verification remains elusive. Traditional electrical transport struggles to discern these lifetimes, as resistivity is largely unaffected by electron scattering. Here, we demonstrate that high-order cyclotron resonance (CR) offers a direct probe: The linewidth of the mth CR peak directly reflects the relaxation rate γ_{m}=1/τ_{m} of the corresponding angular harmonic. Combining theory and terahertz photoconductivity measurements in graphene, we show that the third-order CR exhibits a narrower linewidth than the second-order CR, yielding τ_{3}>τ_{2}. This hierarchy defies conventional impurity or phonon scattering models, instead aligning with TFL predictions where odd harmonics evade relaxation via head-on collisions. Our results provide definitive evidence for the TFL regime and establish high-order CR as a powerful tool to unravel hydrodynamic transport in quantum materials.