Structural Investigations of the Peierls Transitions in TTF-TCNQ and Related Compounds (TSEF-TCNQ, HMTTF-TCNQ, NMP-TCNQ)

Organic Conductors: From Charge Density Wave TTF−TCNQ to Superconducting (TMTSF)2PF6

“…As far as precursor structural effects are concerned, there are significant differences between TTF−TCNQ and TSeF−TCNQ. While precursor effects are 1D in TTF−TCNQ in almost the entire temperature domain where they are observed, the picture is different in TSeF−TCNQ, since short range 3D coupling is observed between 29 and 50 K and only limited 2D coupling is noticed up to 200 K. , Commensurability between CDWs and the underlying lattice (×3) has been detected at 6 kbar through a small peaking of the Peierls transition and a concomitant drop of the longitudinal conductivity …”

“…This is the case for hexamethylene-donor molecules with sulfur or selenium heteroatoms, HMTTF or HMTSF, respectively, , where metallicity is nearly achieved at low temperature. In HMTTF−TCNQ, an incommensurate CDW system with ρ = 0.72, a semimetallic character can be maintained at low temperature under pressure above 19 kbar with δρ/δ T > 0, although a weak transition is still observed in resistivity at 30 kbar . It was anticipated that the complete suppression of the distortion would require a pressure between 35 and 40 kbar.…”

Quasi one-dimensional organic conductors: from Fröhlich conductivity and Peierls insulating state to magnetically-mediated superconductivity, a retrospective

“…As far as structural precursor effects are concerned there are significant differences between TTF-TCNQ and TSF − TCNQ. While precursor effects are one-dimensional in TTF-TCNQ over almost the entire temperature domain where they are observed, the picture is different in TSF − TCNQ since a short range 3D coupling is observed between 29 and 50 K and only a limited 2D coupling is noticed up to 100 K [155,157].…”

“…This is the case for hexamethylene-donor molecules with sulfur or selenium heteroatoms, HMTTF or HMTSF respectively [65,160] where metallicity is nearly achieved at low temperature. In HMTTF − TCNQ, an incommensurate CDW system with ρ = 0.72 [157], a semimetallic character can be maintained at low temperature under pressure above 19 kbar with δρ/δT > 0 although a weak transition is still observed in resistivity at 30 kbar [161]. It was anticipated that the complete suppression of the distortion would require a pressure between 35 and 40 kbar.…”