Spin-liquid and magnetic phases in the anisotropic triangular lattice: The case ofκ−(ET)2X

Abstract

The two-dimensional Hubbard model on the anisotropic triangular lattice, with two different hopping amplitudes t and t ′ , is relevant to describe the low-energy physics of κ-(ET)2X, a family of organic salts. The ground-state properties of this model are studied by using Monte Carlo techniques, on the basis of a recent definition of backflow correlations for strongly-correlated lattice systems. The results show that there is no magnetic order for reasonably large values of the electron-electron interaction U and frustrating ratio t ′ /t = 0.85, suitable to describe the non-magnetic compound with X=Cu2(CN)3. On the contrary, Néel order takes place for weaker frustrations, i.e., t ′ /t ∼ 0.4 ÷ 0.6, suitable for materials with X=Cu2(SCN)2, Cu[N(CN)2]Cl, or Cu[N(CN)2]Br.

Coulomb enhancement of superconducting pair-pair correlations in a34-filled model forκ−(BEDT-TTF)2X

“…As mentioned above, previous works have shown (i) suppression of pair-pair correlations within the effective ρ = 1 model [17][18][19][20] , and (ii) the possibility of a fluctuating CO within models focusing on the monomer molecules 33,34,[36][37][38] . We therefore construct pair creation operators that allow unequal charge densities on the monomer molecules that constitute a dimer in Fig.…”

“…A necessary condition for SC within any interacting electrons model however is that interactions must enhance superconducting pair-pair correlations relative to the noninteracting model. Precise numerical calculations within the 1 2 -filled band Hubbard model on triangular lattices have shown that pair-pair correlations decrease with Hubbard U for all anisotropy [17][18][19][20] , thus indicating the need for going beyond the effective 1/2-filled band model in our search for the the mechanism of SC in κ-(ET) 2 X.…”

Paired electron crystal: Order from frustration in the quarter-filled band

“…Recall that within existing mean field theories the AFM-to-SC transition is driven by spin fluctuations [13][14][15][16][17][18][19][20][21][22][23] , while the CO-to-SC transition is driven by charge fluctuations 65 . Even if we ignore that recent precise numerical calculations [25][26][27] have demonstrated the absence of SC within the proposed spin-fluctuation models in this context (thereby raising doubts also about mean-field theory of charge-fluctuation mediated superconductivity), different mechanisms of SC for structurally related materials with identical or nearidentical molecular components appear to be unrealistic. Within our proposed scenario, the charge-ordered or VBS systems that exhibit SC are PECs in the semiconducting state, while the AFM systems under pressure transform to PECs first and then to SC (although due to actual crystal structures the "width" of the PEC region could be narrow to vanishing within the latter).…”

“…It has been claimed that this transition explains the SC in the CTS [13][14][15][16][17][18][19][20][21][22][23][24] . Recent numerical work by us and others, however, have determined that SC is absent within the ρ = 1 triangular lattice Hubbard model [25][26][27] and the earlier results are artifacts of mean-field approximations.…”

Temperature dependence of structural and electronic properties of the spin-liquid candidateκ-(BEDT-TTF)2Cu2(CN)Jeschke1, Souza2, Valentí3 et al. 2012Phys. Rev. B

“…17 Theoretically, the spin-liquid properties have been investigated on the basis of the anisotropic triangularlattice Hubbard Hamiltonian. 12,[18][19][20][21] The parameters t, t ′ and U of this Hamiltonian have been determined with semi-empirical 7 as well as first principles methods 22,23 based on the experimental structure at room temperature. Missing in such investigations is, however, the consideration of a possible temperature dependence of the model parameters.…”