ESR PROPERTIES OF KAPPA-TYPE ORGANIC SUPERCONDUCTORS BASED ON BEDT-TTF

A systematic investigation of electron spin resonance (ESR) properties, the spin susceptibility (chi(spin)), peak-to-peak linewidth (Delta H-pp) and g-value, of kappa-type BEDT-TTF superconductors has been carried out in order to clarify their electronic structures in the normal state. kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br (Space group: Pnma) and kappa'-(BEDT-TTF)(2)Cu-2(CN)(3)(P2(1)/c) have almost temperature independent g-values along all the crystal axes. On the other hand, the salts with space group of P2(1), kappa-(BEDT-TTF)2Cu(NCS)(2), K-(BEDT-TTF)(2)Cu(CN)[N(CN)(2)] and kappa-(BEDT-TTF)(2)Ag(CN)(2).H2O, were found to show an anomalous enhancement of g-shift below about 130 K when the field was applied along the b axis in the two-dimensional conducting plane. Simultaneously, a rapid broadening of the linewidth has been observed. We discuss possible mechanisms of the anomalous temperature dependence of the g-value for the compounds of the P2(1) space group.