Pulse-duration memory effect in NbS3 and comparison with numerical simulations of phase organization

The oscillatory response of the 59 K charge density wave (CDW) in NbSe3 to a sequence of current pulses was investigated as a function of pulse height and pulse width. Of the 16 samples investigated, seven clearly exhibited t he learned behavior commonly referred to as the pulse-duration memory effec t (PDME). These seven samples. after training, learned the length of the pu lse, and always finished the pulse at a minimum in the voltage oscillation (maximum CDW velocity). Contrary to previous reports, we observe the PDME f or pulse heights much greater than threshold. We find that as the number of metastable states accessible to the CDW during the low portion of the driv e pulse is decreased, the PDME degrades. We summarize the qualitative diffe rences between the theory of phase organization and the observed experiment al data. To facilitate this comparison we have performed numerical simulati ons of the Fukayama-Lee-Rice (FLR) model in both the weak and strong pinnin g limits in an attempt to reproduce the learned response. We find no eviden ce for phase organization (no learning) in the weak pinning limit; also the wave forms generated in the strong pinning limit differ qualitatively from the experimental data. This comparative study suggests that the theoretica l description of the PDME requires further investigation, and the importanc e of amplitude collapse and boundary conditions demand future examination.