Neutral-ionic phase transition of (BEDT-TTF)(ClMeTCNQ) under pressure - art. no. 085106

Observation and characterization are reported on a neutral-ionic (NI) phase transition under pressure in (BEDT-TTF)(ClMeTCNQ), which is a mixed-stack charge-transfer compound with BEDT-TTF-based intercolumnar networks. Optica l and electrical experiments revealed that the compound undergoes a pressur e-induced NI transition at 1 GPa at room temperature. The temperature-press ure phase diagram of this phase transition was established by the electrica l resistivity measurements at low temperature under pressure. The observed symmetry breaking in the infrared spectra and dramatic decrease of resistiv ity indicate that the NI transition in (BEDT-TTF)(ClMeTCNQ) at 1 GPa at roo m temperature is qualitatively similar in nature to that in the standard ma terial (TTF)(CA). In contrast, the NI transition in (BEDT-TTF)(ClMeTCNQ) at low temperature under lower pressure considerably differs from that in (TT F)(CA) as to the resistivity behaviors around the phase boundary: The forme r becomes almost continuous without showing any anomaly, while the latter i s significantly discontinuous. We discuss the origin of the observed electr ical behaviors in (BEDT-TTF)(ClMeTCNQ) in terms of the effect of intercolum nar interaction associated with BEDT-TTF moieties.