Magnetic correlations and superconductivity in La_1.93 Sr_0.07 CuO₄ revealed by μSR

We have performed transverse field muon spin rotation experiments on a single-crystal La_1.93Sr_0.07CuO₄, which is close to the critical value x = 0.06, in the field range from 1 to 60 kOe in order to investigate the relation between magnetism and superconductivity in an underdoped high-T_c superconductor. The measured sample shows evidence of static magnetism at T_g ∼ 4 K, far below the superconducting transition temperature T_c = 17 K. We measured the shift and the linewidth of the fast-Fourier transform (FFT) spectra obtained in a high field of 60 kOe, both of which are dominated by Cu - 3 d spins. The temperature dependences of the shift and the linewidth indicate the development of modulated staggered correlations below 100 K. We conclude that the static staggered correlations coexist with superconductivity far below T_c.