Revisiting the 63Cu NMR Signature of Charge Order in La1.875Ba0.125CuO4

We use single crystal 63Cu NMR techniques to revisit the early 63Cu NQR signature of charge order observed for La1.875Ba0.125CuO4 (Tc = 4 K) [A. W. Hunt et al., Phys. Rev. Lett. 82, 4300 (1999)]. We show that the growth of spin correlations is accelerated below ∼80 K, where the inverse Laplace transform (ILT) T1 analysis of the 139La NMR spin–lattice relaxation curve recently uncovered emergence of the slow components in the lattice and/or charge fluctuations [P. M. Singer et al., Phys. Rev. B 101, 174508 (2020)]. From the accurate measurements of the 63Cu NMR signal intensity, spin echo decay M(2τ), spin–lattice relaxation rate 631/T1, and its density distribution function P(631/T1), we also demonstrate that charge order at Tcharge \( \simeq \) 54 K turns on strong enhancement of spin fluctuations within charge ordered domains, thereby making the CuO2 planes extremely inhomogeneous. The charge ordered domains grow quickly below Tcharge, and the volume fraction FCA of the canonical domains unaffected by charge order gradually diminishes by ∼35 K. This finding agrees with our independent estimations of FCA based entirely on the 139La ILTT1 analyses, but is in a stark contrast with much slower growth of charge ordered domains observed for La1.885Sr0.115CuO4 from its Tcharge \( \simeq \) 80 K to Tc \( \simeq \) 30 K.