Superconductivity and phase separation in La2CuO4+x single crystals

We report a neutron and Raman scattering study of a single-crystal of La2CuO4.05 prepared by high temperature electrochemical oxidation. Elastic neutron scattering measurements show the presence of two phases, corresponding to the two edges of the first miscibility gap, all the way up to 300 K. An additional oxygen redistribution, driven by electronic energies, is identified at 250 K in Raman scattering (RS) experiments by the simultaneous onset of two-phonon and two-magnon scattering, which are fingerprints of the insulating phase. Elastic neutron scattering measurements show directly an antiferromagnetic ordering below a Néel temperature of TN = 210 K. The opening of the superconducting gap manifests itself as a redistribution of electronic Raman scattering below the superconducting transition temperature, Tc = 24 K. A pronounced temperature-dependent suppression of the intensity of the (100) magnetic Bragg peak has been detected below Tc. We ascribe this phenomenon to a change of relative volume fraction of superconducting and antiferromagnetic phases with decreasing temperature caused by a form of a superconducting proximity effect.

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“…These are the same conditions used for crystal L2 in Ref. 26. The oxygen excess δ was estimated to ∼ 0.05.…”

Section: Methodsmentioning

confidence: 95%

Interplay of structural and electronic phase separation in single-crystallineLa2CuO4.05studied by neutron and Raman scattering

et al. 2004

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“…it is strongly increased by the presence of planar defects. 19 In La 2 CuO 4+x single crystals prepared by the molten solution method 20 oxygen mobility is very low due to the small number of defects and hence the scale of the structural separation can be minimized. The single crystal with x = 0.02 prepared by this way appears homogeneous below 200 K in X-ray and neutron studies, 21 although the composition is inside the miscibility gap.…”

mentioning

confidence: 99%

Mesoscopic phase separation inLa2CuO4.02:A
Nikolaev
¹
,
Brom
²
,
Zakharov
³

2000
Phys. Rev. B
5
0
4
0
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In crystals of La2CuO4.02 oxygen diffusion can be limited to such small length scales, that the resulting phase separation is invisible for neutrons. Decomposition of the 139 La NQR spectra shows the existence of three different regions, of which one orders antiferromagnetically below 17 K concomitantly with the onset of a weak superconductivity in the crystal. These regions are compared to the macroscopic phases seen previously in the title compound and the cluster-glass and striped phases reported for the underdoped Sr-doped cuprates.PACS numbers: 74.72.Dn, 75.30.Ds, 75.40.Gb Inhomogeneous carrier and spin distributions in high-T c compounds might be related to phase separation and stripes, 1,2 and are intensively studied especially in hole doped La 2 CuO 4 . In underdoped La 2−x Sr x CuO 4 for x > 0.06 doping leads to spin-density wave order or stripe formation, as seen by neutron scattering at various x-values. 3-6 Recent NQR and NMR studies have revealed new interesting features, like line intensity suppression caused by spin/charge fluctuations, stripe condensation at low temperatures under favorable pinning conditions, and the presence of inequivalent copper sites attributed to a stripe formation. 7-10 At very low Sr content (x < 0.02) the magnetic properties are explained in terms of hole segregation, 11-14 and the formation of a cluster spin glass (x=0.06). 15 For La 2 CuO 4+x the presence of the mobile oxygen dopants leads to a macroscopic structural phase separation in antiferromagnetic (AF) and superconducting (SC) regions in the concentration range 0.01 < x < 0.06 (the so called miscibility gap). [16][17][18] The oxygen mobility is linked to lattice imperfections, e.g. it is strongly increased by the presence of planar defects. 19 In La 2 CuO 4+x single crystals prepared by the molten solution method 20 oxygen mobility is very low due to the small number of defects and hence the scale of the structural separation can be minimized. The single crystal with x = 0.02 prepared by this way appears homogeneous below 200 K in X-ray and neutron studies, 21 although the composition is inside the miscibility gap. In the crystal a superconducting transition is observed around 15-17 K with a very weak diamagnetic signal. 21,22 According to µSR 21 part of the sample becomes magnetically ordered below the same temperature of 15 K, but neutron diffraction does not see any long range magnetic structure. Apparently phase separation happens, but the scale is too small to be visible by standard structural methods. 21 By performing NQR on the same La 2 CuO 4.02 single crystal, we will demonstrate the existence of three regions with different oxygen concentrations and show only one (oxygen-poor) phase to have an antiferromagnetic transition. We evaluate the size of the antiferromagnetic regions from the reduction of staggered magnetization. By comparison with the macroscopic phases seen previously in the title compound 17 and the clusterglass and striped phases seen in La 1.94 Sr 0.06 CuO 4 and La 2−x−y Sr x Eu y CuO...

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“…The opening of a "spin pseudogap" on the Fermi surface was connected at first with strong AFM correlations. But later the propositions that the formation of the pseudogap as well as superconductivity are associated with charge ordering (dynamic analog of phase separation) were discussed (see reviews [1,2]) and were experimentally confirmed [3,4]. Simple example of charge ordering was observed in Bi2212, where in the Cu-O plane metallic (met-) stripes with orthorombic structure and the stripes of the dielectric (di-) tetrogonal phase with a short range AFM correlations were found out at T < T ch (T ch is the temperature of charge ordering) [5].…”

mentioning

confidence: 99%

Charge ordering in quasi-two-dimensional high-temperature superconductors

Sergeeva

2000

Low Temperature Physics

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Superconductivity and phase separation in La2CuO4+x single crystals

Cited by 24 publications

References 12 publications

Interplay of structural and electronic phase separation in single-crystallineLa2CuO4.05studied by neutron and Raman scattering

Interplay of structural and electronic phase separation in single-crystallineLa2CuO4.05studied by neutron and Raman scattering

Mesoscopic phase separation inLa2CuO4.02:A
Nikolaev
¹
,
Brom
²
,
Zakharov
³

2000
Phys. Rev. B
5
0
4
0
View full text Add to dashboard Cite

Charge ordering in quasi-two-dimensional high-temperature superconductors

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Superconductivity and phase separation in La2CuO4+x single crystals

Cited by 24 publications

References 12 publications

Interplay of structural and electronic phase separation in single-crystallineLa2CuO4.05studied by neutron and Raman scattering

Interplay of structural and electronic phase separation in single-crystallineLa2CuO4.05studied by neutron and Raman scattering

Mesoscopic phase separation inLa2CuO4.02:ANikolaev1, Brom2, Zakharov3 2000Phys. Rev. B5040View full textAdd to dashboardCite

Charge ordering in quasi-two-dimensional high-temperature superconductors

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Mesoscopic phase separation inLa2CuO4.02:A
Nikolaev
¹
,
Brom
²
,
Zakharov
³

2000
Phys. Rev. B
5
0
4
0
View full text Add to dashboard Cite