THE LOW-TEMPERATURE PHASE OF ALPHA-(BEDT-TTF)(2)KHG(SCN)(4) .1. ANGLEAND TEMPERATURE-DEPENDENCE OF THE SHUBNIKOV-DEHAAS AND DE-HAAS-VAN-ALPHEN OSCILLATIONS

The magnetoresistance and magnetization of single crystals of the orga nic charge transfer salt alpha-(BEDT-TTF)(2)KHg(SCN)(4) (where BEDT-TT F is bis(ethylenedithio)tetrathiafulvalene) have been studied in field s of up to 30 T and at temperatures as low as 20 mK. Five separate ser ies of quantum oscillations have been observed in the low-temperature, low-field phase of this material and have been studied as a function of tilt angle of the field. It is proposed that two of these frequenci es are the result of Stark quantum interference while the others are S hubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) oscillations due to closed Fermi surface pockets or conventional magnetic breakdown. Th e unconventional temperature dependence observed for some of these osc illations and the applicability of current models of the Fermi surface of alpha-(BEDT-TTF)(2)KHg(SCN)(4) are discussed.