How a ’vegetable ion’ helped scientists unlock theory behind transitions of materials

A puddle freezing on the sidewalk, your humidifier pumping out water vapor, salt trucks melting icy streets-wintertime in Chicago is full of examples of a physics phenomenon called a "phase transition," in which a material changes state. Physicists are fascinated by this phenomenon, which is useful in technology from the basic steam turbine all the way to MRIs. In a paper published Dec. 18 in the journal  Nature,  renowned University of Chicago physicist Peter Littlewood and colleagues propose the most complete picture to date of the transition from conductor to insulator in a type of material called transition metal oxides. Notably, they propose an explanation for a process that had previously baffled theorists, regarding an unexpected role by a part of the molecule called a "vegetable ion." Such oxides have fascinated scientists because of their many attractive electronic and magnetic properties; the discovery may boost the search for new technologies, such as better batteries and electronics.  "Tuning and control of this metal-insulator transition has been the source of much exciting new physics and promising materials applications, such as low-power and ultrafast microelectronics," said Littlewood, who has a joint appointment in Argonne National Laboratory 's Materials Science division. A type of material called a correlated oxide is widely useful; scientists have reaped many insights by studying what happens when these oxides change from conducting electricity with little or no resistance (that is, metal-like) to not conductive (i.e., an insulator).