For a long time, it has been thought that two-dimensional (2D) Fermi gases could support long-lived excitations, owing to the collinear quasiparticle scattering controlled by phase-space constraints at a 2D Fermi surface. We present a direct calculation that reveals such excitations. The excitation lifetimes are found to exceed the fundamental bound set by the Landau Fermi-liquid theory by a factor as large as ${(T_F/T)}^{\alpha }$ with $\alpha \approx 2$. These excitations represent Fermi-surface modulations of an odd parity, one per each odd angular momentum. To explain this surprising behavior, we employ a connection between the linearized quantum kinetic equation and the dynamics of a fictitious quantum particle moving in a 1D reflectionless ${\mathrm{sech}}^2$ potential. In this framework, we identify the long-lived excitations in Fermi gases as zero modes that arise from supersymmetry.

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• Quasiparticles & collective excitations
• Transport phenomena
• Two-dimensional electron system
• Boltzmann theory
• Fermi liquid theory