MIT physicists have trapped electrons in a pure crystal, marking the first achievement of an electronic flat band in a three-dimensional material. The results provide a new way for scientists to explore rare electronic states in 3D materials.
"Trapping electrons in a crystal" is such a nonsensical way of conveying the idea of a flat band. Most isolated crystals trap all the electrons they have inside of them, or else the world will be full of free roaming electrons!