Phase diagram of organic superconductor kappa-(ET)(2)Cu[N(CN)(2)]Br as it is seen from isothermal resistance relaxation

Abase diagram of kappa-(ET)(2)Cu[N(CN)(2)]Br superconductor was studied by resistance measurements of structural relaxation kinetics and properties of nonequilibrium phases after isochronous annealing. We show, that (1) the a ctivation energy of the lattice relaxation time below 100 K corresponds wel l to the potential barrier heights for ET molecule conformation (2) the sha pe of the diagram corresponds to that of the ethylene ordering phenomena wi th superstructure formation (3) the known anomalies of the electronic prope rties of the salt, namely resistance hump at around 100 K and pseudogap beh avior at 60 K correspond to upper and lower hysteresis branches of the ethy lene transformation, while the main second order phase transition proceeds at 80 K; (4) the state that comes our of the transformation is not an order ed state, but rather contains superstructure interacting with the Fermi sur face and causing its partial destruction. We discuss these findings, togeth er with high superconducting T-C, and negative isotope effect as indication s of crucial soft lattice contribution to the superconducting properties in organics.