Collinear scattering and long-lived excitations in two-dimensional electron fluids

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 (TF/T )alpha with alpha ti 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 sech2 potential. In this framework, we identify the long-lived excitations in Fermi gases as zero modes that arise from supersymmetry.