Delving into manganite conductivity

At ambient conditions, manganites have insulating properties, meaning they do not conduct electric charges. When pressure of about 340,000 atmospheres is applied, these compounds change from an insulating state to a metallic state, which easily conducts charges. Scientists have long debated about the trigger for this change in conductivity.

The research team's new evidence, to be published online by Physical Review Letters on Friday, shows that for the manganite LaMnO₃, this insulator-to-metal transition is strongly linked to a phenomenon called the Jahn-Teller effect. This effect actually causes a unique distortion of the compound's structure. The team's measurements were carried out at the Geophysical Laboratory.

Counter to expectations, the Jahn-Teller distortion is observed until LaMnO3 is in a non-conductive insulating state. Therefore, it is reasonable to believe that the switch from insulator to metal occurs when the distortion is suppressed, settling a longstanding debate about the nature of manganite insulating state. The formation of inhomogeneous domains—some with and some without distortion—was also observed. This evidence suggests that the manganite becomes metallic when the breakdown of undistorted to distorted molecules hits a critical threshold in favor of the undistorted.

"Separation into domains may be a ubiquitous phenomenon at high pressure and opens up the possibility of inducing colossal magnetoresistance by applying pressure" said Baldini, who was with Stanford at the time the research was conducted, but has now joined Carnegie as a research scientist.

Provided by Carnegie Institution