Evidence for competing magnetic instabilities in underdoped YBa_{2}Cu_{3}O_{6+x} (original) (raw)
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Antiferromagnetic order in YBa_ {2} Cu_ {3-x} Co_ {x} O_ {6+ y}
1988
We present a neutron scattering study of oxygen-deficient YBa2Cu3-Co"06+~where, with increasing Co concentration, long-range antiferromagnetic order develops on the chain sites. For x 0.2, two magnetic transitions are found: Below T~2 211 K, there is an ordered moment on both Cu sites, awhile for T&2& T(T&I 415 K only a "plane" moment is present. For x 0.8, an ordered moment appears on both Cu sites with a single transition at 435 K. Evidence for magnetic ordering was also found by magnetic susceptibility measurements. These results imply that Co substitution enhances antiferromagnetic coupling between the "plane" and "chain" sites. While the mechanism responsible for superconductivity in the new high-temperature superconducting oxides is still not understood, current theories suggest that electron pairing may arise from antiferromagnetic (AF) correlations. Experimentally, it is found that long-range antiferromagnetic order exists in the nonsuperconducting parent compounds, La2Cu04y (Ref. 2) and YBa2Cu306+y
arXiv (Cornell University), 2005
A magnetically-ordered state is known to exist in and around the vortex cores of under-doped high-Tc superconductors. Here using muon spin rotation, we identify the core state in low-doped YBa2Cu3Oy (y = 6.50) as the same antiferromagnetic state that forms in the bulk of the insulating parent compound YBa2Cu3O6.0. The antiferromagnetic order occurs only where superconductivity is suppressed, and the ordered Cu moment does not depend on the applied magnetic field between 5 and 15 kOe. We also find that the vortex core size in YBa2Cu3Oy increases with under-doping, and that Tc exhibits a sublinear dependence on the inverse square of the in-plane magnetic penetration depth 1/λ 2 ab .
arXiv preprint arXiv:0803.0484, 2008
Abstract: We describe from advanced first principles calculations the energetics of oxygen doping and its relation to insulator-metal transitions in underdoped YBa $ _2 $ Cu $ _3 $ O $ _ {6+ x} .Wefindastrongtendencyofdopingoxygenstoorderintonon−magneticCu. We find a strong tendency of doping oxygens to order into non-magnetic Cu .Wefindastrongtendencyofdopingoxygenstoorderintonon−magneticCu^{1+} $ O $ _x $ chains at any $ x .Orderingproducesone−dimensionalmetallicbands,whileconfigurationswithnon−alignedoxygensareinsulating.TheCu. Ordering produces one-dimensional metallic bands, while configurations with non-aligned oxygens are insulating. The Cu .Orderingproducesone−dimensionalmetallicbands,whileconfigurationswithnon−alignedoxygensareinsulating.TheCu^{2+} $ O $ _2 $ planes remain insulating and antiferromagnetic up to a threshold between $ x $= 0.25 and ...
Physical Review Letters, 2009
We present a neutron-scattering study of the static and dynamic spin correlations in the underdoped high-temperature superconductor YBa 2 Cu 3 O 6.45 in magnetic fields up to 15 T. The field strongly enhances static incommensurate magnetic order at low temperatures and induces a spectral-weight shift in the magnetic-excitation spectrum. A reconstruction of the Fermi surface driven by the field-enhanced magnetic superstructure may thus be responsible for the unusual Fermi surface topology revealed by recent quantumoscillation experiments.
ANTIFERROMAGNETIC ORDERING AND PHASE DIAGRAM OF YBa2Cu3O6+x
Le Journal de Physique Colloques
Neutron scattering experiments on single crystals have allowed an accurate determination of the magnetic phase diagram of YBa2C~306+x. With increasing oxygen content the antiferromagnetic ordering of YBa2Cu306 and TN remain unchanged up to x = 0.2. For x > 0.2 both TN and the ordered moment of c u 2 + ions in the Cu(2) site decrease and vanish abruptly around z z 0.40. The CU+ ions in the Cu(1) site do not order for any oxygen content. For x = 0.30 a reentrant behaviour is observed. Preliminary inelastic neutron scattering experiments on a rather large single crystal (0.2cm3) with x z 0.3 are reported.
Antiferromagnetic Ordering in Superconducting YBa2Cu3O6.5
Physical Review Letters, 2001
Commensurate antiferromagnetic ordering has been observed in the superconducting high-T c cuprate YBa2Cu3O6.5 (Tc=55 K) by polarized and unpolarized elastic neutron scattering. The magnetic peak intensity exhibits a marked enhancement at Tc. Zero-field µSR experiments demonstrate that the staggered magnetization is not truly static but fluctuates on a nanosecond time scale. These results point towards an unusual spin density wave state coexisting with superconductivity.
Coexistence of antiferromagnetic order and spin glass freezing in YBa2 (Cu0.88Fe0.12)3O6.5
Physica C: Superconductivity, 1991
We have performed neutron diffraction, inelastic neutron scattering and M0ssbauer measurements in a semiconducting deoxygenated YBaE(CUosaF%.~2)3Oy (y-~ 6.5) sample. A 3D antiferromagnetic order is observed, with a (~½~) peak and a N6el temperature of 430 K. The magnetic structure, alternating antiferromagnetic (AF) sheets with similar moment values on both Cu I and Cu II sites, coexists with static and dynamical disorder, induced by frustrated Fe spins in the Cu I chains. On lowering the temperature, the Fe spins undergo a spin glass transition below Tr~ 70 K. Concomitantly, the AF order shows a reentrant behavior, characterized by a slight decrease of the ( ½ ½ ~ ) peak intensity. The results are discussed in comparison with undoped deoxygenated compounds.
Low-energy spin fluctuations in YBa2Cu3O6.1 and ErBa2Cu3O6+x A Cu (1) T1 NQR study
Physica C: Superconductivity, 1994
63Cu( 1 ) NQR signals and their relaxation have been measured in YBa2Cu306.1 and ErBa2CuaO6+x at temperatures between 10 K and 300 K. In YBa2Cu306.1 a peak is observed in the spin-lattice relaxation, T/-~, around 140 K. An explanation in terms of doped-hole motion is presented and alternative O (4)-O (5) diffusion mechanisms are critically discussed. In ErBa2Cu306+x the low-temperature T i-1 is dominated by magnetic fluctuations of Er; quantitative agreement is found when the correct ground state and magnetic dynamic properties of the rare earth are taken into account.
Spin susceptibility in underdoped YBa2Cu3O6+x
Physical Review B - PHYS REV B, 2000
We report a comprehensive polarized and unpolarized neutron scattering study of the evolution of the dynamical spin susceptibility with temperature and doping in three underdoped single crystals of the YBa2Cu3O6+x high temperature superconductor: YBa2Cu3O6.5 (Tc=52 K), YBa2Cu3O6.7 (Tc=67 K), and YBa2Cu3O6.85 (Tc=87 K). The spin susceptibility is determined in absolute units at excitation energies between 1 and 140 meV and temperatures between 1.5 and 300 K. Polarization analysis is used extensively at low energies. Transitional matrix elements, including those between spin states, in a bilayer system such as YBa2Cu3O6+x can be generally classified into even and odd, according to the sign change under a symmetry operation that exchanges the layers, and both even and odd excitations are detected in YBa2Cu3O6.5 and YBa2Cu3O6.7. While the even spin excitations show a true gap which depends on doping, the odd spectrum is characterized by a weakly doping-dependent pseudogap. Both even and...