Superconductivity In La2CuO4 Research Articles

Percolative superconductivity in La2CuO4.06 by lattice granularity patterns with scanning micro x-ray absorption near edge structure

The simplest cuprate superconductor La2CuO4+y with mobile oxygen interstitials exhibits a clear phase separation. It is known that oxygen interstitials enter into the rocksalt La2O2+y spacer layers forming oxygen interstitials rich puddles and poor puddles but only recently a bulk multiscale structural phase separation has been observed by using scanning micro X-ray diffraction. Here we get further information on their spatial distribution, using scanning La L3-edge micro X-ray absorption near edge structure. Percolating networks of oxygen rich puddles are observed in different micrometer size portions of the crystals. Moreover, the complex surface resistivity shows two jumps associated to the onset of intra-puddle and inter-puddles percolative superconductivity. The similarity of oxygen doped La2CuO4+y, with the well established phase separation in iron selenide superconductors is also discussed.

Chemical Oxidation of La2CuO4 Epitaxial Thin Films Grown byPulsed Laser Deposition

Chemical oxidation is used to induce superconductivity inLa2CuO4 expitaxial thin films fabricated by pulsed laserdeposition technique. Details about the influence of oxidation time onstructural, surface morphology, Raman spectra, and electricalproperties have been investigated. The results convince that successfuluptake of oxygen occurs in the oxidized films, and the content of theinserted oxygen increases with increasing oxidation interval. Thepossible mechanism for the excess oxygen insertion into the film isalso discussed.

Stripe correlation of tilts and superconductivity in La2CuO4+Σ

In single crystal La2CuO4+Σ,Σ ≈ 0.015, c-axis interstitial oxygen ordering (staging) in the oxygen-rich phase of the phase-separated sample was observed through satellite peaks in the neutron scattering which first appear at 250 K. If the sample is cooled through the temperature region around 210 K over a period of several hours, these satellite peaks show splitting in the a*-direction. This first-order phase transition involves a periodic one-dimensional modulation of the in-plane order. Microscopic modeling leads to a picture where the excess oxygen, and therefore also the doped holes, order in stripes along the a-direction in addition to staging along the c-direction. This ordering in stripes can be regarded as a continuation of the phase separation but now on a local scale, leading to a local increase in oxygen and hole density. This increase can account for the increase of the superconductingT c of 2.5 K observed in our sample and also for many previously reported annealing experiments.

Studies of New Superconductors Revive Old Questions

Lanthanum copper oxide, which is now regarded as the prototype for the new high‐temperature superconductors, undergoes a phase transition to an antiferromagnetic state. The critical temperature for this transition, at which the magnetic moments on copper ions begin to order antiferromagnetically, depends sensitively on the oxygen concentration. Confirmation of the existence of this antiferromagnetic phase in La2CuO4−y and the determination, using neutron scattering, of the arrangement of magnetic moments in it provided definitive evidence last summer for the importance of magnetic phenomena in the new superconducting oxides. Philip Anderson (Princeton University) had proposed in January 1987 that superconductivity in La2CuO4−y doped with barium or strontium, which had been confirmed only two months earlier, arose from novel, short‐range antiferromagnetic correlations between copper spins.

Neutron Diffraction Studies of High TC Superconductors

ABSTRACTWe have investigated the structure and composition of La2CuO4 (both pure and Sr-doped) and Nd(Ba2−xNdx)Cu3O7 using powder neutron diffraction. In La2−xSrxCuO4, Tc reacnes its maximum at x=0.15, after which vacancies are introduced in the 2D planes and superconductivity is destroyed. Superconductivity in La2CuO4 is not bulk. No evidence for nonstoichlometry in this material can be observed. In the Nd(Ba2−xNdx)Cu3O7 system, Tc is a complex function of oxygen ordering and electronic effects.