Coexistence of SDW and Purely-Electronic CDW in Quarter-Filled Organic Conductors

Abstract

We have performed a mean field calculation in order to determine the ground state of a modified Hubbard model of a quarter-filled one-dimensional chain. It is found that the coexistence of 2 k F spin density wave (SDW) and purely-electronic 2 k F charge density wave (CDW) is realized due to the effect of next-nearest-neighbor Coulomb repulsion. Phase diagrams are obtained as the values of nearest- and next-nearest-neighbor Coulomb interaction energies are varied. Competition between the two coexistent states with 2 k F CDW and 4 k F CDW is revealed, which gives a first order transition. Our result supports the X-ray result confirming the presence of a coexisting phase of purely-electronic 2 k F CDW and 2 k F SDW in (TMTSF) 2 PF 6 , a quarter-filled one-dimensional chain in terms of holes.