80K ANOMALY AND ITS EFFECT ON THE SUPERCONDUCTING AND MAGNETIC TRANSITION IN DEUTERATED KAPPA-(BEDT-TTF)(2)CU[N(CN)(2)]BR

In this paper, we report careful transport and magnetic measurements o n single crystals of deuterated kappa-(ET)(2)Cu[N(CN)(2))]Br. By cooli ng the sample at different rates, it is found that cooling through 80 K has a dramatic effect on the normal state metal-insulator transition and the superconducting transition temperatures. In-plane resistivity depends strongly on the cooling rate for temperatures below 80 K, abo ve which all resistivity curves cooled at different rates converge. By comparing it with the nondeuterated salt and the quasi-ID Bechgaard s alt, we speculate that 80 K corresponds to a structural phase transiti on in the anion chain. Fast cooling through 80 K will freeze the high temperature magnetic phase to low temperatures and the presence of loc al magnetic moments suppresses the superconducting T-c.