DEHAAS-VANALPHEN STUDY OF THE CHARGE-TRANSFER SALT ALPHA-(BEDT-TTF)(2)KHG(SCN)(4) IN PULSED MAGNETIC-FIELDS OF UP TO 54 T

The de Haas-van Alphen effect has been measured in the organic conduct or alpha-(BEDT-TTF)(2)KHg(SCN)(4) in pulsed magnetic fields of up to 5 4 T, temperatures down to 350 mK, and at three different angles. Analy sis of the amplitude of the quantum oscillations within the framework of a two-dimensional Lifshitz-Kosevich model reveals that this materia l appears to be only fully transformed into the high-field state at fi elds above similar to 27 T, where the quasiparticle scattering rate is observed to be low. On entering the low-field state, the scattering r ate is observed to increase dramatically. We also observe an apparent increase in the effective mass from similar to 1.5m(e) in the low-fiel d state to similar to 2.7m(e) in the high-field state. The data at low fields are in accord with previous studies, but the nature of the hig her harmonics of the de Haas-van Alphen oscillations at high fields ap pears to signify a departure from conventional Lifshitz-Kosevich behav ior.