Direct observation of a one-dimensional static spin modulation in insulatingLa1.95Sr0.05CuO

Abstract

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.

Two-dimensional incommensurate and three-dimensional commensurate magnetic order and fluctuations in La2−xBaxCuO

“…We observe a linear relationship δ ∼ x for x = 0.125, 0.025, and 0.035, which extrapolates back through zero at x = 0. This conclusion is somewhat different from that reached in previous studies of La 2−x Sr x CuO 4 , wherein a linear δ ∼ x relationship was also found for sufficiently large x, but δ was ∼ independent of x for very low concentrations < 0.02, which also displayed 3D C AF order 44,46 .…”

Neutron scattering studies of Zn-doped La2−xSrxCuO4

“…• Transition from Parallel to Diagonal SDW coincides with the appearance of superconductivity at x c ∼ 0.055 [24,27].…”

“…Wakimoto et al have employed a narrower instrumental Q resolution and succeeded in ascribing a certain magnetic peak to a certain twin; in a single twin, there exist only two satellites with the modulation vector along the orthorhombic b * axis as shown in Fig. 2(b) [24]. These works indicate that the SDW modulation is diagonal to the Cu-O-Cu axis for the x = 0.05 insulating sample, and suddenly turns to be parallel to the direction upon crossing the insulator-to-superconductor phase boundary at x c ∼ 0.055.…”

Theory of anisotropic hopping transport due to spiral correlations in the spin-glass phase of underdoped cuprate superconductors

“…6,7 On the theoretical side it was argued that ξ is finite due to topological defects that lead to frustration of the longrange spiral order. 12,13 Since the localization length is less than the magnetic scale, 1/κ < ξ, we expect that the effective description of transport properties, developed below in terms of the one-hole wave function, is quantitatively valid also at finite (small) doping (i.e.…”

“…However for x < 1/8 and in Nd-free LSCO, charge order has not been detected, while IC magnetism persists down to x ≈ 0.02. 6,7 Thus while IC magnetic order is generically observed in the underdoped regime, static charge order seems to be confined to the neighborhood of x = 1/8. 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 000000000 Theoretically the IC magnetism in the cuprates is often modeled as originating from static charge stripes, and since these are not universally present, one is forced to introduce additional concepts, such as "fluctuating" stripes, electronic liquid crystals, etc.…”