Correlation Effects on Charge Order and Zero-Gap State in the Organic Conductor α-(BEDT-TTF)2I3

Abstract

The effects of electron correlation in the quasi-two-dimensional organic conductor α-(BEDT-TTF)2I3 are investigated theoretically by using an extended Hubbard model with on-site and nearest-neighbor Coulomb interactions. A variational Monte Carlo method is applied to study its ground-state properties. We show that there appears a nonmagnetic horizontal-stripe charge order in which nearest-neighbor correlation functions indicate a tendency toward a spin-singlet formation on the bonds with large transfer integrals along the charge-rich stripe. Under uniaxial pressure, a first-order transition from the nonmagnetic charge order to a zero-gap state occurs. Our results on a spin correlation length in the charge-ordered state suggest that a spin gap is almost unaffected by the uniaxial pressure in spite of the suppression of the charge disproportionation. The relevance of these contrasting behaviors in spin and charge degrees of freedom to recent experimental observations is discussed.

arXiv comment15 pages, 9 figures, accepted for publication in J. Phys. Soc. Jpn

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• Interaction-induced quantum spin Hall insulator in the organic Dirac electron system $\alpha$-(BEDT-TSeF)${}_2$I${}_3$
• Gap opening mechanism for correlated Dirac electrons in organic compounds $\alpha$-(BEDT-TTF)${}_2$I${}_3$ and $\alpha$-(BEDT-TSeF)${}_2$I${}_3$
• Domain Wall Conductivity with strong Coulomb interaction of two-dimensional massive Dirac Electrons in the Organic Conductor $\alpha$-(BEDT-TTF)${}_2$I${}_3$
• Structural and electronic properties of $\alpha ,\beta$-(BEDT-TTF)${}_2$I${}_3$ and $\kappa$-(BEDT-TTF)${}_2$X${}_3$ (X=I,F,Br,Cl) organic charge transfer salts
• Effect of Coulomb Interaction on Seebeck Coefficient of Organic Dirac Electron System $\alpha$-(BEDT-TTF)${}_2$I${}_3$
• Dynamical phase transitions in the photodriven charge-ordered Dirac-electron system
• Possible Spin-Density Wave on Fermi Arc of Edge State in Single-Component Molecular Conductors [Pt(dmdt)${}_2$] and [Ni(dmdt)${}_2$]
• Fragment-orbital-dependent spin fluctuations in the single-component molecular conductor [Ni(dmdt)${}_2$]
• Role of hydrogen bonding in charge-ordered organic conductor $\alpha$-(BEDT-TTF)${}_2$I${}_3$ probed by ${}^{127}$I nuclear quadrupole resonance