期刊
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN
卷 72, 期 6, 页码 1469-1475出版社
PHYSICAL SOC JAPAN
DOI: 10.1143/JPSJ.72.1469
关键词
charge order; extended Hubbard model; mean-field approximation
Phase diagrams of charge order patterns of the theta-phase organic conductors are investigated on the basis of the static-limit extended Hubbard model including the second nearest Coulomb repulsion V. Since the theta-phase is close to the triangular lattice rather than the square lattice, a 3-fold non-stripe charge order is stable in a considerably large region between the stripe phases and the uniform phase. At finite temperatures, such unevenly ordered patterns as the 3-fold phase D+D21/4+ become more stable than the evenly ordered stripes, (D+D0), and it is unlikely that the stripe phase directly transforms to the uniform phase. These results suggest the existence of an unevenly ordered pattern in the metallic state of theta-(BEDT-TTF)(2)RbM(SCN)(4) [BEDT-TTF: bis(ethyleneditho)tetrathiafulvalene, M = Zn and Co] above T-MI = 190 K, accounting for the observation of modulated structures in the X-ray measurement, broadening of the NMR line, flat temperature dependence of the resistivity, and the first-order character of the 190 K transition.
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