Narrow band noise in the SDW state of (TMTSF)2PF6

Narrow band noise has been studied in the SDW phase of (TMTSF)2PF6 in a magnetic field. Strong and weak periodic peaks are clearly observed. The spectrum largely changes with increasing current and depends on applied magnetic field. The fundamental frequency of the current oscillations comes from a sliding motion of the SDW condensate. The strong periodic peaks appear at the harmonic frequencies of this fundamental and move to lower frequency at large currents. This is interpreted in terms of the coexistence with the CDW collective excitation.