Coexistence of superconductivity and magnetic order in YBa2Cu4O8 (original) (raw)
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Physical Review Letters, 2004
We performed zero and transverse field µSR experiments on a large number of YBa2Cu3O6+x samples. We detect coexistence of antiferro-type (AF) short range magnetism with superconductivity below T f 10 K in compositions 0.37 x 0.39. Most muons experience local AF fields, even when SQUID detects a full superconducting volume fraction, which points to a local minimal interference organization of short AF stripes embedded in the superconductor. A detailed phase diagram is produced and the consequences of the minimal interference are discussed.
Arxiv preprint arXiv: …, 2011
The pressure dependence of the magnetic penetration depth λ in polycrystalline samples of YBa2Cu3Ox with different oxygen concentrations x = 6.45, 6.6, 6.8, and 6.98 was studied by muon spin rotation (µSR). The pressure dependence of the superfluid density ρs ∝ 1/λ 2 as a function of the superconducting transition temperature Tc is found to deviate from the usual Uemura line. The ratio (∂Tc/∂P)/(∂ρs/∂P) is factor of ≃ 2 smaller than that of the Uemura relation. In underdoped samples, the zero temperature superconducting gap ∆0 and the BCS ratio ∆0/kBTc both increase with increasing external hydrostatic pressure, implying an increase of the coupling strength with pressure. The relation between the pressure effect and the oxygen isotope effect on λ is also discussed. In order to analyze reliably the µSR spectra of samples with strong magnetic moments in a pressure cell, a special model was developed and applied.
Muon spin rotation evidence for a glassy superconducting state in YBa2Cu3O7-y
Physics Letters A, 1988
We report on muon spin rotation (IISR) measurements of the internal magnetization in polycrystalline samples of the high Ts uperconductor YBa2Cu3O7_~. The mean value as well as the mean square deviation of the internal magnetic field seen by the muons undergo large variations with temperature. This effect shows a marked dependence on the magnetic history of the sample, which is what is expected of a glassy superconducting state.
Pressure-Induced Superconductivity in Elemental Ytterbium Metal
Physical Review Letters
Ytterbium (Yb) metal is divalent and nonmagnetic (4f 14 configuration). Under pressure its valence increases significantly leading to the expectation that magnetic instabilities and other highly correlated electron effects may appear before a stable trivalent state is reached (4f 13 configuration). We carried out electrical resistivity and ac magnetic susceptibility measurements to 179 GPa over the temperature range 1.4-295 K. No evidence for magnetic order is observed. However, Yb becomes a superconductor at 86 GPa with Tc ≃ 1.4 K, increasing to 4.6 K at 179 GPa. X-ray absorption spectroscopy shows that Yb remains mixed-valent to at least 125 GPa, pointing to an active role of f electrons in the emergence of superconductivity in this simple, elemental solid.
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.
Hyperfine Interactions, 1991
Zero-field muon-spin-rotation (μSR) measurements on (Y1−x Prx )Ba2Cu3O7 [x=1.0, 0.8, 0.6, and 0.54] show evidence for antiferromagnetic ordering of the Cu moments within the Cu−O planes, with Néel temperatures 285, 220, 35. 30 and 20 K, respectively. Forx=1.0 the local muon magnetic field is ≈16 mT, but decreases to ≈12 mT at 17K, due to additional magnetic ordering. The zero-field data, in conjunction with transport data, allow construction of a complete phase diagram for this system. Transverse-field (1 kOe) μSR data forx=0.2 (T c =75 K) show that the muon depolarization is determined primarily by the Cu nuclear moments forT>T c , and by the vortex state forT<T c . Fitting the superconducting-state data to a BCS model yields an extrapolated zero-temperature magnetic penetration depth of 2170 Å.
Physical Review B, 2011
A new NMR anvil cell design is used for measuring the influence of high pressure on the electronic properties of the high-temperature superconductor YBa2Cu4O8 above the superconducting transition temperature Tc. It is found that pressure increases the spin shift at all temperatures in such a way that the pseudo-gap feature has almost disappeared at 63 kbar. This change of the temperature dependent spin susceptibility can be explained by a pressure induced proportional decrease (factor of two) of a temperature dependent component, and an increase (factor of 9) of a temperature independent component, contrary to the effects of increasing doping. The results demonstrate that one can use anvil cell NMR to investigate the tuning of the electronic properties of correlated electronic materials with pressure.
2009
Combined synchrotron angle-dispersive powder diffraction and micro-Raman spectroscopy are used to investigate pressure-induced lattice instabilities that are accompanied by superconducting Tc anomalies in YBa2Cu4O8 and optimally doped YBa2Cu3O 7−δ , in comparison with the nonsuperconducting PrBa2Cu3O6.92. In the first two superconducting systems there is a clear anomaly and hysteresis in the evolution of the lattice parameters and increasing lattice disorder with pressure, which starts at ≈ 3.7 GPa. On the contrary, in the Pr-compound the lattice parameters follow very well the expected equation of state (EOS) up to 7 GPa. The micro-Raman data of the superconducting compounds show that the energy and width of the Ag phonons exhibit anomalies over the same pressure range where the lattice parameters deviate from the EOS and the average Cu2-O pl bond length exhibits a strong contraction that correlates with the non-linear pressure dependence of Tc. The anomalous Raman behavior is not observed for the non superconducting Pr compound, clearly indicating a connection with the charge carriers. It appears that the cuprates close to optimal doping are at the edge of lattice instability.