The melting of crystals has resisted efforts to understand the microscopic process for more than a century. The course of the struggle has stimulated the development of quantum mechanics, concepts of long-range order, the role of dimensionality in condensed matter, surface physics, and more sensitive experimental techniques to test the theories. After years of probing the mechanism within the bulk material, we learn that the answer has been lying on the surface.

DOI:https://doi.org/10.1103/RevModPhys.71.1737