Revisiting the ${}^{63}$Cu NMR signature of charge order in La${}_{1.875}$Ba${}_{0.125}$CuO${}_4$

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 $M(2\ddot{I}„)$, 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.

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