"139La NMR investigation of the charge and spin order in a La1.885Sr0.115CuO4 single crystal"

A. Arsenault: S. K. Takahashi , T. Imai, W. He and Y. S. Lee, M. Fujita ; Physical Review B, 02/14/18.

Additional Authors: S. K. Takahashi , T. Imai, W. He and Y. S. Lee, M. Fujita

Abstract:

139La NMR is suited for investigations into magnetic properties of La2CuO4-based cuprates in the vicinity of their magnetic instabilities, owing to the modest hyperfine interactions between 139La nuclear spins and Cu electron spins. We report comprehensive 139La NMR measurements on a single-crystal sample of high-Tcsuperconductor La1.885 Sr0.115 CuO4 in a broad temperature range across the charge and spin order transitions (Tcharge ≃ 80 K, T neutron spinTc = 30 K). From the high-precision measurements of the linewidth for the nuclear spin Iz = +1/2 to −1/2 central transition, we show that paramagnetic line broadening sets in precisely at Tcharge due to enhanced spin correlations within the CuO2 planes. Additional paramagnetic line broadening ensues below ∼35 K, signaling that Cu spins in some segments of CuO2 planes are on the verge of three-dimensional magnetic order. A static hyperfine magnetic field arising from ordered Cu moments along the ab plane, however, begins to develop only below T μSR spin = 15–20 K, where earlier muon spin rotation measurements detected Larmor precession for a small volume fraction (∼20%) of the sample. Based on the measurement of 139La nuclear-spin-lattice relaxation rate 1/T1, we also show that charge order triggers enhancement of low-frequency Cu spin fluctuations inhomogeneously; a growing fraction of 139La sites is affected by enhanced low-frequency spin fluctuations toward the eventual magnetic order, whereas a diminishing fraction continues to exhibit a behavior analogous to the optimally superconducting phase even below Tcharge. These 139La NMR results corroborate our recent 63Cu NMR observation that a very broad, anomalous winglike signal gradually emerges below Tcharge, whereas the normally behaving, narrower main peak is gradually wiped out [T. Imai et al., Phys. Rev. B 96, 224508 (2017)]. Furthermore, we show that the enhancement of low-energy spin excitations in the low-temperature regime below T neutron spin (≃Tc) depends strongly on the magnitude and orientation of the applied magnetic field.