LIGHT, PRESSURE, AND STRESS-INDUCED PHASE-TRANSITIONS OF DEUTERATED CU(DCNQI)(2) RADICAL-ION SALTS

The extremely sharp metal-insulator phase transition at T-c = 60 K of g-fold deuterated Cu(DCNQI)(2) could be shifted to lower temperature T by illumination with Light and by mechanical tension, both acting con trarily to the application of pressure. By proper selection of T, usin g pressure cycles, the samples could be switched to a persistent insul ating state. Applying light (of different wavelengths) we could reesta blish the conductivity. Correlating the temperature dependence of the crystal length (interferometric, resolution Delta l/l < 10(-5)) with t hat of the conductivity clearly demonstrates by the smooth change of t he crystal length the model of connectivity Limited conductivity betwe en the noninverted still metallic microdomains.