The hierarchy of excitation lifetimes in two-dimensional Fermi gases

Abstract

In this thesis we show that omentum-conserving quasiparticle collisions in two-dimensional Fermi gases give rise to a large family of exceptionally long-lived excitation modes. The lifetimes of these modes exceed by a factor (TF/T)2 >> 1 the conventional Landau Fermi-liquid lifetimes T ~ TF/T2. The long-lived modes have a distinct angular structure, taking the form of cos m6 and sin mO with odd m values for a circular Fermi surface, with relaxation rate dependence on m of the form m4 log m, valid at not-too-large m. In contrast, the even-m harmonics feature conventional lifetimes with a weak m dependence. The long-time dynamics, governed by the long-lived modes, takes the form of angular (super)diffusion over the Fermi surface. Altogether, this leads to unusual long-time memory effects, defining an intriguing transport regime that lies between the conventional ballistic and hydrodynamic regimes.