Revisiting the $^{63}$Cu NMR signature of charge order in La$_{1.875}$Ba$_{0.125}$CuO$_{4}$

TL;DR

This study uses advanced NMR techniques on single crystals to analyze charge order and spin fluctuations in La$_{1.875}$Ba$_{0.125}$CuO$_{4}$, revealing rapid domain growth and inhomogeneity below charge ordering temperature.

Contribution

It provides detailed NMR evidence of charge order onset and domain evolution in La$_{1.875}$Ba$_{0.125}$CuO$_{4}$, highlighting differences with similar cuprates.

Findings

Charge order appears at ~54 K with enhanced spin fluctuations.

Charge ordered domains grow rapidly below T_charge, reducing unaffected volume fraction.

Inhomogeneity within CuO$_2$ planes increases due to charge order.

Abstract

We use single crystal $^{63}$Cu NMR techniques to revisit the early $^{63}$Cu NQR signature of charge order observed for La$_{1.875}$Ba$_{0.125}$CuO$_{4}$ ($T_{\text{c}} =4$~K) [A. W. Hunt et al., Phys. Rev. Lett. {\bf 82}, 4300 (1999)]. We show that the growth of spin correlations is accelerated below $\sim 80$~K, where the inverse Laplace transform (ILT) T$_{1}$ analysis of the $^{139}$La NMR spin-lattice relaxation curve recently uncovered emergence of the slow components in the lattice and/or charge fluctuations [P. M. Singer et al., {\bf 101}, 174508 (2020)]. From the accurate measurements of the $^{63}$Cu NMR signal intensity, spin echo decay $M(2\tau)$, spin-lattice relaxation rate $^{63}1/T_1$, and its density distribution function $P(^{63}1/T_{1})$, we also demonstrate that charge order at $T_{\text{charge}}\simeq 54$~K turns on strong enhancement of spin fluctuations {\it within charge ordered domains}, thereby making the CuO$_2$ planes extremely inhomogeneous. The charge ordered domains grow quickly below $T_{\text{charge}}$, and the volume fraction $F_{\text{CA}}$ of the canonical domains unaffected by charge order gradually diminishes by $\sim 35$~K. This finding agrees with our independent estimations of $F_{\text{CA}}$ based entirely on the $^{139}$La ILTT$_{1}$ analyses, but is in a stark contrast with much slower growth of charge ordered domains observed for La$_{1.885}$Sr$_{0.115}$CuO$_{4}$ from its $T_{\text{charge}}\simeq 80$~K to $T_{\text{c}}\simeq 30$~K.