Charge order, spin order, and spin gap in coupled ladder system -AVO (A=Na, Sr)

Seo, Hitoshi; Ishibashi, Shoji*

Electronic properties of -AVO (A=Na, Sr) are investigated theoretically. By calculating their band structures within GGA first-principles method and deriving effective tight-binding models by numerical fitting to them, we find that their electronic state is composed of two different two-leg ladders which are coupled three-dimensionally, with average of 1/6 electron per V site for A=Na and 1/3 electron per V site for A=Sr, consistent with previous studies. We investigate the mechanism of novel charge ordering patterns observed in these compounds, and that of spin ordering in the Na compound and the spin gap formation in the Sr compound, by introducing on-site Coulomb interaction into the tight-binding models, i.e., considering Hubbard models. Effects of cation ordering, which is found to affect the physical properties in the metallic phases of both compounds, are also discussed.