Patrick Irvin

Think of a stack of paper: when the sheets lie perfectly aligned, light passes through them uniformly. But turn one sheet by a few degrees, and the picture changes. Something similar happens with layers in certain materials: rotate them relative to each other, and their properties change — sometimes dramatically. Spectroscopy isn't the key here, or rather, it's not the method used.

In a dark room, a spark jumps between two wires, and for an instant, there is light. Physicists have done something similar, but a million times smaller: at the boundary of two transparent crystals, they drew a conducting path and left a break just a few atoms wide. When a direct voltage was applied across this tiny gap, it began to glow.