Classical physics predicted that messy defects in a crystal would merely scatter moving electrons like pinballs; Philip Anderson proved that quantum wave interference traps electrons in place, freezing electrical currents completely. Awarded the 1977 Nobel Prize in Physics, Anderson Localization unlocked the physics of disordered materials, topological insulators, and light-trapping photonic metamaterials.

In classical electrical physics, if a metal crystal has random impurities and defects, moving electrons are expected to bounce off them like pinballs in an obstacle course, slowing down the electrical current into electrical resistance. No one imagined that adding defects could stop electricity from moving entirely.
Bell Labs theoretical physicist Philip Anderson treated electrons as quantum waves. He proved that when waves travel through a disordered maze of random atomic defects, their reflections interfere destructively with each other—canceling out all forward motion and trapping the electron frozen in a tiny pocket of space.
Anderson's paper founded the modern quantum physics of disordered systems. By explaining how semiconductors turn from metals into insulators, by enabling optical fibers that trap and guide light pulses with disorder, and by guiding quantum computing circuits, Anderson localization reshaped condensed matter physics.
Absence of Diffusion in Certain Random Lattices
This paper presents a simple model for such processes as spin diffusion or conduction in the "impurity band." These processes involve transport in a lattice which is in some sense random, and in them diffusion is expected to take place via quantum jumps between localized sites. In this simple model the essential randomness is introduced by requiring the energy to vary randomly from site to site. It is shown that at low enough densities no diffusion at all can take place, and the criteria for transport to occur are given.
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