Abstract
We report the results of an extensive elastic neutron-scattering study of the incommensurate (IC) static spin correlations in 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 at positions rotated by in reciprocal space from those found in superconducting samples. The present neutron-scattering experiments on the same 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 This has made possible the precise characterization of the IC elastic peaks around and (orthorhombic notation) in each domain separately. We find that, in a single twin, only two satellites are observed at and that is, the modulation vector is only along the orthorhombic axis. This demonstrates unambiguously that has a one-dimensional 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 crystal that previously was reported to show a single commensurate peak. By mounting the sample in the zone, we have discovered that the sample in fact has the same IC structure as the sample. The incommensurability parameter for and 0.05, where is the distance from in tetragonal reciprocal lattice units, follows the linear relation These results demonstrate that the insulator to superconductor transition in the underdoped regime in 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.
- Received 9 August 1999
DOI:https://doi.org/10.1103/PhysRevB.61.3699
©2000 American Physical Society