In metals like copper and aluminium, conduction electrons move around freely, in the same way as particles in a gas or a liquid.
But when impurities are introduced into the metal's crystal lattice, electrons cluster together in a uniform pattern around the point of interference, resembling the ripples that occur when a stone is thrown into a pool of water. Scientists have now discovered how to strengthen these Friedel oscillations and focus them, almost like using a lens, in different directions.
They've discovered (Nature Communications, DOI: 10.1038/ncomms6558) that at a range of 50 nanometers, these "giant anisotropic charge density oscillations" are many times greater than normal.