The low-temperature phase of : I. Angle and temperature dependence of the Shubnikov - de Haas and de Haas - van Alphen oscillations

The magnetoresistance and magnetization of single crystals of the organic charge-transfer salt (where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) have been studied in fields of up to 30 T and at temperatures as low as 20 mK. Five separate series 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 frequencies are the result of Stark quantum interference while the others are Shubnikov - de Haas (SdH) and de Haas - van Alphen (dHvA) oscillations due to closed Fermi surface pockets or conventional magnetic breakdown. The unconventional temperature dependence observed for some of these oscillations and the applicability of current models of the Fermi surface of are discussed.