Document Type


Publication Date

January 1995


Dynamic electron spin resonance (ESR) and extended x-ray absorption edge fine structure (XAFS) measurements suggest that layered organic metals and cuprate superconductors behave similarly. The response to microwave radiation in a modulated external magnetic field indicates that: (i) triplet state, T * ESR is observed below Tc for both; (ii) the condensation of free spin doublet D to T* occurs above the transition temperature to superconductivity Tc (10 ± 1 K for the organic metal (BEDT-TTF)3Ta2F11 and 92 to 12 K for YBa2Cu3O7-δ and its rare earth derivatives); (iii) antiferomagnetic (AF) resonance is detected above Tc for the organic metal. Here the exchange field between the aligned AF domains: JAF(150 K) = 130.7 mT (153 mK) is greater than the exchange term J(150 K) ≈ 15 mT (20 mK) between free spins (S = 1/2) leading to T* states; the lifetime of AF domains τAFdecreases below 150 K and resonance is not detected below 44 K (i.e. τAF < 10-10 s) allowing a superconducting transition to appear below 10 K; (iv) the relaxation time τ1 for the half field, triplet state ESR absorption increases fourfold near 10 K for the organic metal and, (v) the onset of superconductivity is detected in all superconductors by the appearance of an energy loss at exactly H=0 and, magnetization oscillations observed versus H below Tcwhen the samples are cooled in a non-zero field H. The spin-lattice relaxation time for the organic metal triplet state, half field ESR near 10 K is interpreted using the Gorter phenomenological relation τ1 = CH /αH, CH and αH are respectively the heat capacity and the thermal contact coefficient to the lattice by the spin system, at constant field H . Complementary changes in x-ray edge widths near Tc are correlated to electron-phonon interactions.


This is a postprint of an article published in Superlattices and Microsturctures Vol 18 in 1995. The version of record can be found here: