RAPID OSCILLATION AND FERMI-SURFACE RECONSTRUCTION DUE TO SPIN-DENSITY-WAVE FORMATION IN THE ORGANIC CONDUCTOR (TMTSF)(2)PF6

Resistance and magnetic torque for the quasi-one-dimensional organic c onductor (TMTSF)(2)PF6 have been measured over a wide magnetic field a nd temperature-ranges to investigate the correlation between the rapid oscillation (RO) and the spin-density-wave (SDW)-formation. The RO wi th the frequency of 220 T is found in the resistance above 15 T for al l the current directions and in the ab-plane Hall resistance in the SD W phase. The RO amplitude has a sharp peak around 3 K, which is associ ated with a maximum of the normalized magnetoresistance. The magnetic torque shows a jump at the SDW transition temperature (similar to 11.5 K) with decreasing temperature, and then a broad maximum around 3 K ( T-max) suggesting a subphase transition. T-max slightly shifts to a hi gh temperature with increasing magnetic field. A possible mechanism of the RO is discussed on the basis of the Fermi surface reconstruction due to the SDW formation.