Static and ESR susceptibilities of the ambient pressure superconductors β- and αt-(BEDT-TTF)2I3 and (BEDT-TTF)2Cu(SCN)2

Abstract

Whereas the static spin-susceptibility χ(T) of β- and αt-(BEDT-TTF)2I3 at 5.7 tesla increases in a slow monotonic manner with temperature, χs(T) for the organic superconductor (BEDT-TTF)2Cu(SCN)2 displays a markedly structured temperature dependence. This gives evidence for two or more phase transitions in the metallic phase at temperatures near 100 K and 50 K, in addition to the onset of superconductivity at 5.7 tesla below not, vert, similar 8 K. Good agreement is found between the absolute magnitudes of static and ESR susceptibility results, thus confirming that orbital susceptibility contributions are of negligible importance here. Cooling in low magnetic fields reveals that superconductivity in (BEDT-TTF)2Cu(SCN)2 sets in at a temperature near 8.5 K, with a 7.6% Meissner effect in 14 G field.