SPATIAL-DISTRIBUTION OF CHARGE-DENSITY-WAVE PHASE-SLIP IN NBSE3

Steady-state charge transport via motion of charge-density waves (CDW' s) requires conversion between collective CDW conduction and quasipart icle conduction in the vicinity of current injection contacts. The con version occurs via phase slip, in which CDW amplitude defects form and move in the presence of CDW strain so as to remove or add CDW phase f ronts in a process analogous to phase slip in superconductors and supe rfluids. We have determined the spatial distribution of phase slip for the T-p1 CDW in NbSe3 by measuring the spatial variation of the CDW c urrent density j(c)(x). As the current contacts are approached. j(c)(x ) decreases and the normal current j(n)(x) due to quasiparticle flow i ncreases. The size of the region near each contact where appreciable p hase slip occurs is less than 40 mu m for T near 120 K but grows to hu ndreds of micrometers at lower temperatures. The current and phase-sli p profiles are asymmetric with respect to driving current direction, i mplying an asymmetry between phase front addition and removal. Analysi s of these profiles yields the local relation between the phase-slip r ate r(ps)(x) and CDW strain epsilon(x). This relation is not unique, a nd for a given strain the phase-slip rate increases with increasing di stance from the current electrode. These results are inconsistent with the predictions of models for phase slip via homogeneous defect nucle ation, and provide evidence for amplitude defect motion. The presence of substantial amounts of phase slip at large distances from the curre nt contacts explains the loss of coherence of the sliding CDW observed at lower temperatures, and suggests that predictions of phase-only mo dels of CDW dynamics may be of very limited use in describing the slid ing CDW in NiSe3.