PRESSURE AND LIGHT EFFECTS ON THE PHASE-TRANSITION OF DEUTERATED CU(2,5-DIMETHYL-DICYANOQUINONEDIIMINE)(2)

The deuterated dicyanoquinonediimine salt Cu(2-CD3,5-CD3-DCNQI)(2), (d (6)), a highly conductive organic metal, exhibits a phase transition f rom the metallic to the insulating state at T-c approximate to 60 K. I n a wide temperature range we observe an anticoincidence of high condu ctivity and electron spin resonance (ESR). These experiments were perf ormed simultaneously in our ESR apparatus equipped for application of He pressure up to 200 bar. Near T-c there is a coexistence of conducti ng (ESR-silent) and insulating (ESR-detectable) domains. This correlat ion of ESR and conductivity sigma points to a percolation limited cond uctivity. Upper and lower limits of the size of the domains are given. Light shifts T-c to lower temperatures, pressure to higher ones. This could be due to shrinking of the lattice which induces the phase tran sition when critical structural parameters are approached. This is mos t probably explained by a simultaneous development of a charge density wave (CDW) and a spin pairing within the DCNQI stack together with th e trimerization of the lattice. Systematic measurements by variation o f temperature, pressure, and light led to phase diagrams of (d(6)) and to the understanding of the mechanism of the phase transitions. (C) 1 996 American Institute of Physics.