Revisiting the ⁶³Cu NMR Signature of Charge Order in La_1.875Ba_0.125CuO₄

We use single crystal ⁶³Cu NMR techniques to revisit the early ⁶³Cu NQR signature of charge order observed for La_1.875Ba_0.125CuO₄(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 spinlattice 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 T_charge≃ 54K turns on strong enhancement of spin fluctuations within charge ordered domains, thereby making the CuO₂planes extremely inhomogeneous. The charge ordered domains grow quickly below T_charge, 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 F_CAbased entirely on the ¹³⁹La ILTT₁analyses, but is in a stark contrast with much slower growth of charge ordered domains observed for La_1.885Sr_0.115CuO₄from its T_charge≃ 80K to T_c≃ 30 K.