Broken symmetry states in quasi-one-dimensional molecular conductors –competitions, co-existences, and frustration –

Abstract

Quasi-one-dimensional molecular conductors with a quarter-filled band exhibit a variety of phase transitions, into different electronic and electron–lattice coupled ordered states accompanying symmetry breaking. To investigate their physical properties especially at finite temperatures and provide a systematic understanding, we study extended Hubbard type models which take account of the effects of interchain Coulomb repulsion, with and without frustration, as well as the electron–lattice couplings. Different theoretical methods, such as mean-field theories, the bosonization and renormalization group scheme, and numerical techniques, are applied in order to capture different features of the experimentally observed ordering phenomena: charge order, lattice dimerization (dimer-Mott insulator), and spin-Peierls lattice tetramerization, showing competitions and different kinds of coexistent states among them.