ESR Properties of κ-Type Organic Superconductors Based on BEDT-TTF

Abstract

A systematic investigation of electron spin resonance (ESR) properties, the spin susceptibility (χ spin ), peak-to-peak linewidth (Δ H pp ) and g -value, of κ-type BEDT-TTF superconductors has been carried out in order to clarify their electronic structures in the normal state. κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br (Space group: Pnma) and κ'-(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 , κ-(BEDT-TTF) 2 Cu(NCS) 2 , κ-(BEDT-TTF) 2 Cu(CN)[N(CN) 2 ] and κ-(BEDT-TTF) 2 Ag(CN) 2 ·H 2 O, 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.