TY - JOUR

T1 - Effects of electron-lattice coupling on charge order in θ-(ET) 2X

AU - Tanaka, Yasuhiro

AU - Yonemitsu, Kenji

PY - 2007/5/1

Y1 - 2007/5/1

N2 - Charge ordering accompanied by lattice distortion in quasi-two dimensional organic conductors θ-(ET) 2X (ET = BEDT-TTF) is studied by using an extended Hubbard model with Peierls-type electron-lattice couplings within the Hartree-Fock approximation. It is found that the horizontal-stripe charge-ordered state, which is experimentally observed in θ-(ET) 2RbZn(SCN) 4, is stabilized by the self-consistently determined lattice distortion. Furthermore, in the presence of the anisotropy in nearest-neighbor Coulomb interactions V ij, the horizontal charge order becomes more stable than any other charge patterns such as diagonal, vertical and 3-fold-type states. At finite temperatures, we compare the free energies of various charge-ordered states and find a first-order transition from a metallic state with 3-fold charge order to the insulating state with the horizontal charge order. The role of lattice degrees of freedom in the realization of the horizontal charge order and the relevance to experiments on θ-(ET) 2X are discussed.

AB - Charge ordering accompanied by lattice distortion in quasi-two dimensional organic conductors θ-(ET) 2X (ET = BEDT-TTF) is studied by using an extended Hubbard model with Peierls-type electron-lattice couplings within the Hartree-Fock approximation. It is found that the horizontal-stripe charge-ordered state, which is experimentally observed in θ-(ET) 2RbZn(SCN) 4, is stabilized by the self-consistently determined lattice distortion. Furthermore, in the presence of the anisotropy in nearest-neighbor Coulomb interactions V ij, the horizontal charge order becomes more stable than any other charge patterns such as diagonal, vertical and 3-fold-type states. At finite temperatures, we compare the free energies of various charge-ordered states and find a first-order transition from a metallic state with 3-fold charge order to the insulating state with the horizontal charge order. The role of lattice degrees of freedom in the realization of the horizontal charge order and the relevance to experiments on θ-(ET) 2X are discussed.

KW - Charge order

KW - Electron-lattice coupling

KW - Extended Hubbard model

KW - Hartree-Fock approximation

KW - Organic conductor

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U2 - 10.1143/JPSJ.76.053708

DO - 10.1143/JPSJ.76.053708

M3 - Article

AN - SCOPUS:34547472179

VL - 76

JO - Journal of the Physical Society of Japan

JF - Journal of the Physical Society of Japan

SN - 0031-9015

IS - 5

M1 - 053708

ER -