  How electrons get accelerated to relativistic energies in a high-Mach-number
quasi-perpendicular shock is presented by means of ab initio particle-in-cell
simulations in three dimensions. We found that coherent electrostatic Buneman
waves and ion-Weibel magnetic turbulence coexist in a strong-shock structure
whereby particles gain energy during shock-surfing and subsequent stochastic
drift accelerations. Energetic electrons that initially experienced the surfing
acceleration undergo pitch-angle diffusion by interacting with magnetic
turbulence and continuous acceleration during confinement in the shock
transition region. The ion-Weibel turbulence is the key to the efficient
nonthermal electron acceleration.
