Quantum Coherence Beyond the Thermal Length

Recent experiments have used scattering to map the flow of electrons in a two-dimensional electron gas. Among other things, the data from these experiments show perseverance of regular interference fringes beyond the kinematic thermal length. These fringes are seen in full quantum-mechanical simulations with thermal averaging, and within the phase coherence length they can also be understood with a simple, single-scattering model. This effect provides a new way to gauge the coherence length independent of thermal broadening. Appealing to higher-order scattering, we present a mechanism by which interference fringes may survive even beyond the phase coherence length.