Charge orders in organic charge-transfer salts

Abstract

Motivated by recent experimental suggestions of charge-order-driven ferroelectricity in organic charge-transfer salts, such as $\kappa$-(BEDT-TTF)${}_2$Cu[N(CN)${}_2$]Cl, we investigate magnetic and charge-ordered phases that emerge in an extended two-orbital Hubbard model on the anisotropic triangular lattice at $3/4$ filling. This model takes into account the presence of two organic BEDT-TTF molecules, which form a dimer on each site of the lattice, and includes short-range intramolecular and intermolecular interactions and hoppings. By using variational wave functions and quantum Monte Carlo techniques, we find two polar states with charge disproportionation inside the dimer, hinting to ferroelectricity. These charge-ordered insulating phases are stabilized in the strongly correlated limit and their actual charge pattern is determined by the relative strength of intradimer to interdimer couplings. Our results suggest that ferroelectricity is not driven by magnetism, since these polar phases can be stabilized also without antiferromagnetic order and provide a possible microscopic explanation of the experimental observations. In addition, a conventional dimer-Mott state (with uniform density and antiferromagnetic order) and a nonpolar charge-ordered state (with charge-rich and charge-poor dimers forming a checkerboard pattern) can be stabilized in the strong-coupling regime. Finally, when electron-electron interactions are weak, metallic states appear, with either uniform charge distribution or a peculiar $12$-site periodicity that generates honeycomb-like charge order.

20 pages, 15 figures

References in corpus (10)

• Spin current and magneto-electric effect in non-collinear magnets
• Multiferroics: different ways to combine magnetism and ferroelectricity
• Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction
• Absence of charge order in the dimerized κ-phase BEDT-TTF salts
• Strong coupling theory of the spinless charges on the triangular lattices: possibility of a new quantum liquid
• Ab initio two-dimensional multiband low-energy models of EtMe_3Sb[Pd(dmit)_2]_2 and κ-(BEDT-TTF)_2Cu(NCS)_2 with comparisons to single-band models
• Ferroelectric properties of charge-ordered alpha-(BEDT-TTF)2I3
• Phase Competition and Superconductivity in $\kappa$-(BEDT-TTF)${}_2$X: Importance of Intermolecular Coulomb Interactions
• Polar Charge Fluctuation and Superconductivity in Organic Conductor
• Spin and Charge Fluctuations near Metal-Insulator Transition in Dimer-Type Molecular Solid

Cited by in corpus (11)

• Critical Spin Liquid versus Valence Bond Glass in Triangular Lattice Organic $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$
• Evidence for electronically-driven ferroelectricity in the family of strongly correlated dimerized BEDT-TTF molecular conductors
• Superconductivity in correlated BEDT-TTF molecular conductors: critical temperatures and gap symmetries
• Mechanism of superconductivity and electron-hole doping asymmetry in $\kappa$-type molecular conductors
• Ingredients for Generalized Models of $\kappa$-Phase Organic Charge-Transfer Salts: A Review
• Charge-Order on the Triangular Lattice: A Mean-Field Study for the Lattice $S=1/2$ Fermionic Gas
• Formation of Spatial Patterns by Spin-selective Excitations of Interacting Fermions
• Thermal algebraic-decay charge liquid driven by competing short-range Coulomb repulsion
• Electronic State and Optical Response in a Hydrogen-Bonded Molecular Conductor
• Multi-orbital two-particle self-consistent approach -- strengths and limitations
• Absence of superconductivity in the Hubbard dimer model for kappa-(BEDT-TTF)_2X