Many strongly correlated electron systems have a domain structure that obscures the fundamental properties of the material. Nanoscale samples, on the other hand, can be smaller than the characteristic domain size, thus making it possible to explore these fundamental properties in detail. Experiments by David Cobden and co-workers on single-domain nanobeams made of vanadium dioxide have revealed several new aspects of the metal-insulator transition in this material, including supercooling of the metallic phase, and a connection between the transition and the equilibrium carrier density in the insulating phase. The cover image, 85 m across, shows vanadium dioxide crystals and nanobeams attached to a silica substrate at 70 °C: the stripes are alternating metallic (darker) and insulating regions.

Cover design by Karen Moore

Letter p420; News & Views p406