Measurement of Unique Magnetic and Superconducting Phases in Oxygen-Doped High-Temperature Superconductors ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_{4+y}$

We present a combined magnetic neutron scattering and muon spin rotation study of the nature of the magnetic and superconducting phases in electronically phase separated ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_{4+y}$, $x=0.04$, 0.065, 0.09. For all samples, we find long-range modulated magnetic order below $T_N\simeq Tc=39\mathrm{K}$. In sharp contrast to oxygen-stoichiometric ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$, we find that the magnetic propagation vector as well as the ordered magnetic moment is independent of Sr content and consistent with that of the “striped” cuprates. Our study provides direct proof that superoxygenation in ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_{4+y}$ allows the spin stripe ordered phase to emerge and phase separate from superconducting regions with the hallmarks of optimally doped oxygen-stoichiometric ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$.

Figure 1

(a)–(c) ENS scans in reciprocal space through the m-AFM peak at $\mathbf{Q}=(1+{\delta }_H,{\delta }_K,0)$. All data were taken at $T=2\mathrm{K}$ at IN14. Solid lines are Gaussian fits and the horizontal red lines show the resolution as found by corresponding scans through structural Bragg peaks. The gray shaded region indicates the average peak position as described in the text. (d) Temperature dependence of the intensity of the m-AFM peaks. Intensities are scaled at 2 K. In order to locate $T_N$, the data are fit to a power law with fixed exponent of 0.5 (lines).

Figure 2

Results of HTF-$\mu \mathrm{SR}$ experiments. If not visible, the statistical errors are smaller than the data point markers. (a)–(c) Temperature dependence of the magnetic and nonmagnetic volume fractions of the sample. Dashed lines are guides to the eye and gray shaded regions mark $T_N$. (d)–(f) Temperature dependence of the spin relaxation rate for muons stopping in the superconducting regions of the sample. Following Ref. 44 the dashed lines are fits to the function ${\sigma }_0(1-aT-b{T}^2)$ for $T<T_c$. Gray shaded regions mark $T_c$.

Figure 3

(a)–(h) Rocking curve scans through the m-AFM peaks of $\mathrm{LSCO}+\mathrm{O}$, $x=0.09$. All lines represent Gaussian fits.