Mott transition in two-dimensional frustrated compounds

The phase diagrams of isotropic and anisotropic triangular lattices with local Coulomb interactions are evaluated within cluster dynamical mean-field theory. As a result of partial geometric frustration in the anisotropic lattice, short-range correlations are shown to give rise to re-entrant behavior which is absent in the fully frustrated isotropic limit. The qualitative features of the phase diagrams including the critical temperatures are in good agreement with experimental data for the layered organic charge-transfer salts $\kappa \text{−}{\left(\text{BEDT-TTF}\right)}_2\text{Cu}\left[\text{N}{\left(\text{CN}\right)}_2\right]\text{Cl}$ and $\kappa \text{−}{\left(\text{BEDT-TTF}\right)}_2{\text{Cu}}_2{\left(\text{CN}\right)}_3$.

Figure 1

(Color online) Phase diagrams of Hubbard model for anisotropic triangular lattice $\left(t^{\prime }=0.8t\right)$ and isotropic triangular lattice $\left(t^{\prime }=t\right)$, evaluated within ED cluster DMFT for $t=0.04\text{eV}$. Plotted are the first-order metal-insulator phase boundaries as functions of inverse local Coulomb energy $U$. In the experimental setup increasing hydrostatic pressure $P$ implies increasing bandwidth $W$ or decreasing $U$. The re-entrant behavior found for $t^{\prime }=0.8t$ is absent in the isotropic limit $t^{\prime }=t$.

Figure 2

(Color online) Nearest-neighbor spin correlations in isotropic and anisotropic triangular lattices for $T=0.05t$, $t^{\prime }=t_{12}$, and $t=t_{13}=t_{23}$. Strong enhancement of spin correlations occurs for moderate deviations from the isotropic limit.

Figure 3

(Color online) Hysteresis behavior of spectral weights $A_i\left(0\right)$ at $E_F=0$ and average double occupancy $d_{\text{occ}}$ as functions of Coulomb energy for anisotropic triangular lattice ($t=1$, $t^{\prime }=0.8t$, and $T=0.05t$). Red solid (blue dashed) curves: increasing (decreasing) $U$.

Figure 4

(Color online) Average spectral distributions of cluster sites below and above the Mott transition for the anisotropic triangular lattice ($t=1$, $t^{\prime }=0.8t$, and $T=0.02t$) for Coulomb energies $U=7.5t$ and $U=8.2t$. The bare density of states is shown by the dashed blue curve.