FERMI-SURFACE STUDIES OF ALPHA-PHASE ORGANIC METALS AND SUPERCONDUCTORS

The present first de Haas-van Alphen (dHvA) experiments on the quasi-t wo-dimensional (quasi-2D) organic metals alpha-(ET)(2)MHg(SeCN)(4) (M = Tl or K) and compare the results with dHvA data of the isostructural organic superconductor alpha-(ET)(2)NH4Hg(SCN)(4). The angular depend ences of the single found dHvA frequency and the field-independent eff ective cyclotron mass, m(c), perfectly follow the 2D 1/cos Theta behav ior, From the observed spin-splitting zeros we unambiguously could ext ract the values of g mu(b). Comparison with m(c) strongly suggests a r educed electron-phonon coupling constant in the nonsuperconducting sal ts.