Phase analysis of non-coherent processes in a moving CDW

Earlier it has been found that the signal produced by a moving CDW contains along with fundamental of narrow band frequency (ω1) and its harmonics (ωn) a non-coherent part—a lot of non-coherent oscillations. Due to a rather broad frequency range the power associated with non-coherent oscillations is comparable to or even greater than that for fundamental frequency, and hence, can play an essential role in CDW dynamics. Now we report on the phase analysis of non-coherent part of the signal produced by moving CDW in thin samples of o-TaS3. To obtain frequency resolved phase characteristics of a signal with fast varying amplitude and abrupt phase jumps the wavelet transform has been performed using complex Morlet functions as a base. It was found that the frequencies from a rather narrow band around ω1 (typically Δω/ω1≈0.25) are tightly locked together and form the main harmonic of narrow band signal. Similarly, the frequencies close to ω2 are also tightly locked. Outside these narrow bands the oscillations are essentially non-coherent. The characteristic feature for these non-coherent oscillations is the following very specific phase synchronization process. Two very close frequency components manifest simultaneous abrupt phase shifts. For one component the phase is shifted by +π (forward), while for the other it is shifted by −π (backward). A most remarkable feature of this locking process is that the resultant phase shift between very close frequency components of non-coherent signal is every time exactly 2π. These observations are considered in terms of CDW velocity redistribution accompanying its motion in an electrical field.