Spectral purity and phase coherence of narrow-band noise in NbSe3

An unusually simple narrow band noise spectrum with a single fundamental and seven harmonics due to depinned charge density wave motion in NbSe₃ is reported. The simplicity of the spectrum is attributed to a very uniform current distribution associated with a short, thin sample of high perfection. The distribution of harmonics is near to that of the sawtooth waveform generated by a relaxation oscillator. As indicated by the amplitude ratio of the fundamental to the first harmonic, this distribution has only a moderate variation over three orders of magnitude in frequency. An electrical relaxation oscillator analog which reproduces most of the properties of CDW motion in NbSe₃ is discussed. A search for phase memory of the narrow band noise in NbSe₃ showed it to be less than one period.