Materials science: Clockwork at the atomic scale.

Abstract

Design rules for exotic materials known as polar metals have been put into practice in thin films. The findings will motivate studies of how a phenomenon called screening can be manipulated to generate new phases in metals. See Letter p.68 The ordered electric dipoles that characterize, for example, ferroelectric materials, are not something generally associated with a metal. Indeed, the free carriers responsible for metallic behaviour will typically eliminate polar ordering, to achieve an equilibrium state of zero net internal electric field (Gauss's law). But the possible existence of a polar state in metals is not fundamentally excluded, and some rare examples exist. Tae Heon Kim and colleagues now use ab initio calculations to identify the structural conditions under which such an exotic state might be stabilized, and then use this information to guide the experimental realization of new room-temperature polar metals.