Neutron-scattering experiments have been performed on lightly-doped La2−xSrxCuO4 single crystals in both the insulating (x = 0.03, 0.04, 0.05) and superconducting (x = 0.06) regions. Elastic magnetic peaks are observed at low temperatures in all samples with the maximum peak linewidth occuring at the critical concentration xc = 0.05. New incommensurate peaks are observed only at x = 0.05, the positions of which are rotated by 45• in reciprocal space about (π, π) from those observed for x ≥ 0.06 in the superconducting phase.PACS numbers: 74.72. Dn, 75.10.Jm, 75.50.Ee, 71.45.Ln, 75.70.Kw The interplay between magnetism and superconductivity has been a central issue in research on high-T c superconductivity for over a decade. Recently Yamada et al.
Measurements of polarized neutron scattering were performed on a S=1/2 chain multiferroic LiCu2O2. In the ferroelectric ground state with the spontaneous polarization along the c axis, the existence of transverse spiral spin component in the bc plane was confirmed. When the direction of electric polarization is reversed, the vector spin chirality as defined by C_(ij)=S_(i)xS_(j) (i and j being the neighboring spin sites) is observed to be reversed, indicating that the spin-current model or the inverse Dzyaloshinskii-Moriya mechanism is applicable even to this e_(g)-electron quantum-spin system. Differential scattering intensity of polarized neutrons shows a large discrepancy from that expected for the classical-spin bc-cycloidal structure, implying the effect of large quantum fluctuation.
We report the results of an extensive elastic neutron-scattering study of the incommensurate ͑IC͒ static spin correlations in La 1.95 Sr 0.05 CuO 4 , which is an insulating spin glass at low temperatures. Recent work by Wakimoto et al. has revealed the presence of new two-dimensional satellite peaks in La 1.95 Sr 0.05 CuO 4 at positions rotated by ϳ45°in reciprocal space from those found in superconducting samples. The present neutron-scattering experiments on the same xϭ0.05 crystal employ a narrower instrumental Q resolution and thereby have revealed that the crystal has only two, rather than four, orthorhombic twins at low temperatures with relative populations of 2:1. This has made possible the precise characterization of the IC elastic peaks around (1,0,0) and (0,1,0) ͑orthorhombic notation͒ in each domain separately. We find that, in a single twin, only two satellites are observed at (1,Ϯ0.064,L) ortho and (0,1Ϯ0.064,L) ortho , that is, the modulation vector is only along the orthorhombic b* axis. This demonstrates unambiguously that La 1.95 Sr 0.05 CuO 4 has a onedimensional rather than two-dimensional static diagonal spin modulation at low temperatures, consistent with certain stripe models. From the L dependence we conclude that the spin correlations are predominantly two dimensional. We have also reexamined the xϭ0.04 crystal that previously was reported to show a single commensurate peak. By mounting the sample in the (H,K,0) zone, we have discovered that the xϭ0.04 sample in fact has the same IC structure as the xϭ0.05 sample. The incommensurability parameter ␦ for x ϭ0.04 and 0.05, where ␦ is the distance from (1/2,1/2) in tetragonal reciprocal lattice units, follows the linear relation ␦Ӎx. These results demonstrate that the insulator to superconductor transition in the underdoped regime (0.05рxр0.06) in La 2Ϫx Sr x CuO 4 is coincident with a transition from diagonal to collinear static stripes at low temperatures thereby evincing the intimate coupling between the one-dimensional spin density modulation and the superconductivity.
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