Charge dynamics near the onset of charge-density-wave (CDW) order in La-124 cuprates

The dynamics of charge-ordered states is one of the central unresolved issues in underdoped cuprate high-temperature superconductors. By measuring nonequilibrium charge transport in La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_{4}$ across the CDW (and structural) transition, we have found evidence for collective dynamics of domains in the CDW-ordered phase: although they are strongly pinned by disorder, the domains are not static, but trapped in long-lived metastable states [1]. Nonequilibrium effects, such as nonexponential relaxations and avalanches in the resistance observed in response to a change in temperature $T$ or magnetic field $H$, are revealed only when the transition is approached from the charge-ordered phase. To isolate the effects of structure and charge order, we have performed similar measurements on La$_{1.7}$Eu$_{0.2}$Sr$_{0.1}$CuO$_{4}$, where CDW ordering at $T=T_{CO}$ does not coincide with the structural transition. We find that, in $H\parallel c$, both materials exhibit a similar onset of negative magnetoresistance near $T_{CO}$, thus attributing that behavior to the onset of charge order. Other similarities and differences in charge transport will also be discussed. [1] P.~G.~Baity \textit{et al.}, arXiv:1609.02591v2 [cond-mat] (2016).