OPTICALLY REVERSED PEIERLS TRANSITION IN CRYSTALS OF CU(DICYANOQUINONEDIIMINE)(2)

A fast photoinduced transient switching of partly deuterated Cu(2,5-di methyl-N,N'-dicyanoquinonediimine)(2) [Cu(DCNQI)(2)] radical ion salt crystals is analyzed as a reversed Peierls transition. Switching from the insulating state into the conducting state is performed on a time scale below 20 ps. Conductivity indirectly proves that the Peierls dis tortion of the insulating phase is efficiently canceled by photoexcita tion. Evaluation of the electrical transients shows that the switched volume can be at least 100 times larger than the directly photoexcited part of the crystals. We propose a reversible structural change which is induced by an acoustic wave traveling through large parts of the s ample volume.