•LaMnO3 insulator-metal transition
Doped manganites have been widely investigated since the colossal magnetoresistance (CMR) effect was discovered at the insulator to metal transition (IMT). This effect promises new technical applications in the field of electronic and spintronic devices. However, understanding, and ultimately controlling, this effect remains a challenge because of competing interactions. LaMnO3, the parent compound of many doped manganites, is the archetype compound because of the strong coupling between lattice, orbital, electronic, and spin degrees of freedom. At ambient conditions, LaMnO3 displays insulating properties so it does not conduct electric charges.
High pressure-low temperature Raman spectroscopy measurements provides the first experimental evidence for the persistence of this distortion within the insulating phase, demonstrating that the IMT is connected with the disappearance of the Jahn-Teller distortion. This study resolves the ongoing debate about the nature of the pressure driven IMT, demonstrating that LaMnO3 become metallic when the distortion is suppressed. Formation of domains of distorted and regular octahedra were observed over the entire insulating phase suggesting a new mechanism behind the IMT transition. Separation into domains opens up the possibility of inducing CMR effect in an undoped sample as LaMnO3 by applying pressure.
For more information, please see: Baldini, M., V. V. Struzhkin, A. F. Goncharov, P. Postorino, and W. L. Mao, “Persistence of Jahn Teller distortion up to insulator to metal transition in LaMnO3”, Phys. Rev. Lett. 106, 066402 (2011).