Effects of the anion ordering superlattice on the ´ raped oscillation ´ in (TMTSF)/sub 2/X

Summary form only given. We discuss on a novel type of magnetic oscillatory phenomenon, so-called the ´rapid oscillation´, observed in quasi-one dimensional organic conductors (TMTSF)/sub 2/X. To clarify its origin, we made magnetotransport studies on (TMTSF)/sub 2/CIO/sub 4/ under high pressures. We found that the rapid oscillation is dramatically suppressed above a threshold pressure about 5kbar. It is known that this compound has a superlattice caused by anion ordering, and it disappears under high pressures. Therefore, the present results strongly suggest that the presence of the superlattice is responsible for the rapid oscillation in (TMTSF)/sub 2/ClO/sub 4/. These results are well understood by the model we previously proposed. Whereas, there is an embarrassing fact that another oscillatory phenomenon was observed under high pressures. It has a period about two times longer than the conventional one. Possible explanations are a)there is another oscillation mechanism independent of the superlattice and b)another superlittice appearing under high pressures causes the other oscillation. To make it clear, we make X-ray studies under high pressures.