BLOCH OSCILLATIONS

Bloch oscillation is a phenomena from solid state physics. It describes the oscillation of a particle (e.g. an electron) if a constant force is acting on it.
If a particle is exposed to a constant force its momentum changes due to Newtons law . The particle accelerates and moves through the periodic lattice potential of the crystal. Think of the lattice potential as an $sin^2$-function.
At the bottom and the wells of the potential the slope changes its sign. Since the slope is related directly related to the (group) velocity of the particle the direction of motion is changed at this points: The particle oscillates (in spatial space).