THERMALLY-INDUCED INSULATOR-METAL TRANSITION IN LACOO3 - A VIEW BASEDON THE MOTT TRANSITION

The thermally induced insulator-metal transition (IMT) has been invest igated for single crystals of undoped and lightly doped LaCoO3 by meas urements of the optical-conductivity spectra, the resistivity, and the Hall coefficient up to 800 K. The IMT around 500 K, where the spin-st ate transition from the nonmagnetic (S = 0) ground state-to the interm ediate-spin (S=1) state is nearly completed, is characterized by a lar ge energy-scale change of the electronic structure as well as by a ste ep increase of carrier number up to a typical metallic value due to cl osing of the charge gap. These behaviors are strikingly parallel to th ose characteristic of the Mott transition.