Inter-chain Coulomb-lattice relaxation and multicriticality in charge transfer organic complexes

We discuss the neutral-to-ionic phase transition and emergence of the multi-criticality in the quasi-one-dimensional charge-transfer salt TTF-CA under pressure. We stress that subtle interplay of Coulomb and lattice processes may be quite sensitive to pressure. Emergence or disappearance of the multi-critical points in a series of charge-transfer salts are understood through this interplay. Whatʹs behind is coexistence and coupling of the non-symmetry-breaking and symmetry-breaking order parameters.