https://phys.org/news/2018-07-extreme-conditions-semiconductors.html

If this state is maintained for too long, the beads will break apart and the crystal dissolves. To analyze Wannier-Stark localization, the physicists had to remove the stabilizing structures, capture the system within a fraction of a light oscillation using light pulses, and finally to stabilize it again to prevent the atoms from breaking apart. The experiment was made possible through the highly intense electric field of an ultrashort infrared light pulse, which is present in the crystal for a few femtoseconds only. "This is what we specialize in: studying phenomena that only exist on very short time scales," explains Alfred Leitenstorfer.

"In perfect insulators and semiconductors, electronic states expand throughout the entire crystal. According to an 80-year-old prediction, this changes as soon as electrical voltage is applied," says Professor Torsten Meier from Paderborn University. "If the electric field inside the crystal is strong enough, the electronic states can be localized to a few atoms. This state is called the Wannier-Stark ladder," explains the physicist.