On the Phase Transition ofα-(ET)2I3

The nature of the metal-insulator (MI) transition of α -(ET) 2 I 3 has been studied theoretically. The effect of the on-site Coulomb interaction has been investigated at absolute zero within the Hartree-Fock approximation. If the Coulomb interaction exceeds some critical value, charge transfer occurs between different stacks and antiferromagnetic spin ordering is stabilized one-dimensionally along one stack, which results in the MI transition. It is also argued that this MI transition will lead to spin-Peierls-like distortion making the ground state nonmagnetic. Hence the present theoretical results offer a possible explanation for the intriguing feature of the MI transition of the title material.