Charge disproportionation in the metallic state of α -(BEDT-TTF)₂I₃

Abstract

13C-NMR measurements have been carried out on the quasi two-dimensional organic conductor, α-(BEDT-TTF) 2 I 3 . We measured the angular dependence of 13 C-NMR spectrum at several temperatures above metal-insulator transition temperature, 135 K (=T MI, ). We found that charge (spin) disproportionation already exists in the metallic state and gradually develops as temperature approaches to T MI .