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The effect of B2O3 addition on La2−xSrxCuO4 (LSCO) single-crystal growth by traveling solvent floating zone technique was examined. Experimentally, it was found that addition of boron oxide to the solvent provides a reduction of the solvent penetration into the feed rod and better seeding. No influence of boron on the superconductivity characteristics of grown LSCO single crystals was found. As a result high-quality, subgrain and inclusion-free La2−xSrxCuO4 single crystals with x=0.0, 0.09 and 0.13 were prepared.

The normal-state magnetotransport properties of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{CuO}}_{4}$ single crystals with $x=0.095$ are measured; at this composition, a structural transition to a low-temperature tetragonal (LTT) phase occurs without suppression of superconductivity. None of the measured properties (in-plane and out-of-plane resistivity, magnetoresistance, and Hall coefficient) shows any sudden change at the LTT phase transition, indicating that the occurrence of the LTT phase does not necessarily cause an immediate change in the electronic state such as the charge-stripe stabilization.

Single-crystalline films of La 2− x Sr x CuO 4 were prepared on nonsuperconducting substrates of Zn-doped La 2 CuO 4 single crystals by the liquid phase epitaxial (LPE) technique. The La 2− x Sr x CuO 4 single-crystalline films, less than 50 μm thick, were subgrain- and crack-free. The Sr content of the La 2− x Sr x CuO 4 films was determined to be 0.07–0.11, but the films were contaminated with less than 3 at.% aluminum as a result of the use of alumina crucibles. Some of the La 2− x Sr x CuO 4 films exhibited superconductivity with T c onset ≈30 K and Δ T c ≈20 K.

Single crystals of La2−xMxCuO4 (MCa, Sr, Ba) were grown by the TSFZ method with an infrared heating furnace. In the TSFZ growth of La2−xMxCuO4, the Sr content was controlled within a wide range as compared with the other dopants. The La2−xMxCuO4 grown crystals had high quality with a sharp superconducting transition.

The electron tunneling spectroscopy is performed on PbILa 1− x Sr x CuO 4 (LSCO) junctions fabricated on high quality LSCO single crystals grown by traveling solvent floating zone (TSFZ) method. For the junctions fabricated parallel to ab -planes, periodic sharp spikes in the spectrum are observed at ∼ 6 × (2 n + 1) mV, where n is a natural number, while for the junctions fabricated on the (001) plane only gap structures corresponding to Pb and LSCO are observed. We ascribe the spike structure to subbands in the electron density of states caused by the Andreev reflections on the periodically modulated gap potential along the c -axis of LSCO.

We report on vector magnetization studies of a La{sub 1.9}Sr{sub 0.1}CuO{sub 4} single crystal, cut in the form of a disk with the anisotropy (c) axis parallel to the disk plane. We observe a sharp threshold in the angular dependences of the isothermal remanent magnetization. When the magnetic field is applied within a threshold angle to the ab plane, the remanent moment is strictly parallel to ab, and also the c-axis component of magnetization is reversible. The threshold angle scales with temperature in the same manner as the lower critical field parallel to the c axis, H{sub c1}{sup c}. These observations give direct support to the presence of a vortex lock-in transition to the CuO planes in our crystal. {copyright} {ital 1997} {ital The American Physical Society}

The paramagnetic (μ-O) state formed at the oxygen site in high Tc LaSrCuO was used to probe an interaction between the localized moment of the paramagnetic electron and the conduction electrons via zero field μ- spin relaxation. The enhanced relaxation rates consistently observed in the superconducting state of various Sr concentrations are explained as an effect of spin‐pairing in the high Tc supercurrent.

Single crystals of pure and Zn-doped CuGeO3 were successfully grown by the FZ and TSFZ methods using an infrared heating furnace. The grown crystals, typically about 5 mm in diameter and 30 mm in length, were crack-free, bright blue and transparent. The effective distribution coefficient of Zn into CuGeO3 was determined to be 0.26 for a Zn concentration of 0.03. Single crystals of Cu1 − xZnxGeO3 with homogeneous composition were grown by the TSFZ method using Zn-rich melts. The as-grown crystals were characterized by magnetization measurements, and the magnetic transitions are discussed.

The paramagnetic state of the muonic atom formed by the negative muon (μ−) bound to the oxygen in highTc LaSrCuO which was found in our recentμ− spin rotation experiments was applied to probe an interaction between the paramagnetic electron and the highTc supercurrent. The observed enhanced spin relaxation rates of the (μ−O) system in the superconducting state revealed the presence of such an interaction.

In order to study these inhomogeneities, Ce-doped and undoped strontium-barium niobate (SBN) fibers were grown by a laser-heated pedestal growth (LHPG) technique in various Ce:Sr x Ba 1− x Nb 2 O 6 compositions along both c [001] and a [100] crystallographic axes. Specific optical inhomogeneities distributed in a radial manner (core effects) are observed in such crystals. Two-dimensional scanning electron microprobe analysis (SEPMA) indicated Ba enrichment and Sr decrease in the cores. An approximate control segregation coefficient (' k oA ) was introduced to characterize the segregation in the fibers. For different cations ' k oSr = 0.98, ' k oBa = 1.04 and ' k oNb = 0.99 were obtained which both determine and demonstrate the complexity of the inhomogeneities in the core in the radial direction.

For the first time the growth of La 2− x Ca x CuO 4 single crystals with 0 ≤ x ≤ 0.1 by the traveling solvent floating zone (TSFZ) method is reported. The grown crystals were homogeneous in composition and free from inclusions. The Ca content in the grown crystals became saturated at about x ≈ 0.1 even though the Ca contents in the feeds and solvents were increased further. Magnetic susceptibilities and electrical resistivities in the ab -plane and along the c -axis reveal significant anisotropy.

We report detailed experimental results on the anisotropic electric resistivity ϱ ( T , x ) for a series of La 2− x Ba x CuO 4−δ single crystals ( x = 0.06, 0.08, 0.09) grown by the TSFZ method. In all as-grown crystals, a semiconducting electric conduction was observed in the normal state both in the ab plane and along the c -axis. After annealing in oxygen, ϱ ab ( T ) became metallic and ϱ c ( T ) remained semiconducting above the superconducting transition temperature. Though the change in T c was small after the annealing, the normal-state resistivity changed significantly. A possible reason for such behaviors was discussed. The resonating valence bond (RVB) model and power law were adopted to fit the experimental data.

Purple Au-Al alloy films were deposited on glass substrates using a radio frequency ion plating method. Au-Al alloys were used as source materials. The effects on the film of the source alloy composition and the evaporation time were studied. The color tones of the deposited films were measured using spectral reflectance and their crystal structures were studied by X-ray diffraction. As a result, a composition of Au 80%-Al 20% was chosed as the most suitable source alloy. The color tone of a film deposited from a single evaporation source changed from white to purple as the evaporation time increased. The intensity of the X-ray diffraction pattern of the AuAl2 sharpened as the color tone of the film became more purpler. The purple color of the film became brighter after 1hour of heat annealing at 550°C in an atmosphere of Ar (8×103Pa).

Single crystals of Ba 1− x Sr x TiO 3 were grown by the floating zone (FZ) method using an infrared heating furnace. The grown crystals of Ba 1− x Sr x TiO 3 , typically 8 mm in diameter and 4 mm in length, were crack-free and yellowish transparent. Substitution of more than 1.2 at% Sr for Ba in BaTiO 3 was effective in preventing the formation of the hexagonal phase. It was found that Ba 1− x Sr x TiO 3 melts congruently at 1.5 at% Sr.

The acoustic phonon modes of the spin-Peierls compound CuGeO 3 have been measured along the principal directions at various temperatures. The longitudinal mode along b*, which is perpendicular to the Cu 2+ chain direction, lies below the transverse mode in the same direction and is quite broad in energy due to damping. Measurements of the spin-excitation spectrum reveal that there remains considerable intensity spreading over a wide energy range above T SP = 14.2 K, and persisting up to about 50 K.

Ultrasonic and specific-heat measurements have been performed on single crystals of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ (LSCO) with x=0.09, 0.14, and 0.19 across the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$. We observed jumplike decreases in the longitudinal elastic moduli at ${\mathit{T}}_{\mathit{c}}$, as are seen in conventional superconductors. Anisotropic strain dependence of ${\mathit{T}}_{\mathit{c}}$ was estimated from both the jump in the elastic moduli and specific heat at ${\mathit{T}}_{\mathit{c}}$ via the Ehrenfest relation. With further lowering temperature below ${\mathit{T}}_{\mathit{c}}$, we found a pronounced lattice stiffening in the elastic moduli of LSCO, which contrasts with the continuous softening observed in most of the conventional superconductors. Thermodynamic analysis revealed that the stiffening originates from the change in the superconducting condensation energy under the lattice strain. This unusual lattice stiffening in the superconducting state is possibly a common character of the high-${\mathit{T}}_{\mathit{c}}$ copper oxides.

The oxygen annealing effect on the temperature-dependent electrical resistivity has been studied in La 1.91 Ca 0.09 CuO 4− y single crystals grown by the TSFZ method. In as-grown crystals, semiconducting-like electrical conduction has been observed, both in the ab -plane and the c -axis at the non-superconducting state. The onset transition temperature T c-onset was about 17.5 K. After annealing in oxygen, ϱ ab ( T ) becomes metallic and shows a resistivity minimum at a certain temperature T min that separates regions of metallic behavior at T > T min from semiconducting behavior at T T min , while ϱ c ( T ) remains semiconducting. In the low-temperature region, an upward curvature of the resistivity (ϱ ab ( T )) has been observed with decreasing temperature below T min . This is an indication of the occurence of weak electron localization due to the randomness of the oxygen distribution the crystal lattice caused by oxygen deficiency that might still be present in the annealed samples. The Anderson-Zou fit to the data works well in metallic samples and the variable range hopping law (VRH) in non-metallic samples.

Phonons and magnetic excitations were studied as a function of temperature in the spin-Peierls phase of an inorganic material ${\mathrm{CuGeO}}_{3}$ by Raman scattering. All of the phonon Raman peaks observed at room temperature can be assigned on condition that the crystal symmetry is ${\mathit{D}}_{2\mathit{h}}^{5}$(Pbmm). Five peaks intrinsic to the spin-Peierls state were observed at 30, 105, 228, 370, and 818 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in the spin-Peierls phase. The temperature dependence of the frequency of the 30-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peak agrees approximately with 2\ensuremath{\Delta}(T), where \ensuremath{\Delta}(T) is the spin-Peierls gap. The Raman spectrum between 0 and 300 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ was compared with the density of states of the magnetic excitons. The 105- and 228-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ peaks were assigned to two-magnetic-exciton Raman scattering. The peaks at 370 and 818 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ were assigned to one-phonon Raman scattering of the folded ${\mathit{A}}_{\mathit{g}}$ modes, which occurs due to the formation of a dimerization in the spin-Peierls phase.

We present resonant ultrasound spectroscopy measurements of the complete elastic moduli of La[sub 2[minus][ital x]]Sr[sub [ital x]]CuO[sub 4] ([ital x]=0.00 and 0.14). The [ital x] dependence of both the absolute values of the moduli in the tetragonal phase and the temperature dependences of the moduli near the structural phase transition is weak. In both materials [ital c][sub 44] and 1/2 ([ital c][sub 11][minus][ital c][sub 12]) are unaffected by the transition, [ital c][sub 33] shows a steplike drop broadened by fluctuations, and [ital c][sub 11] and [ital c][sub 66] decrease as 1/([ital T][minus][ital T][sub SPT]) for [ital T][gt][ital T][sub SPT] (where [ital T][sub SPT] is the structural phase transition temperature). We also present measurements of the anisotropic thermal expansion coefficients in La[sub 1.86]Sr[sub 0.14]CuO[sub 4] using a high-resolution capacitance dilatometer. These data when taken together raise serious questions about the standard interpretation of the structural phase transition in La[sub 2[minus][ital x]]Sr[sub [ital x]]CuO[sub 4].

The dimerization of the Cu ions in the spin-Peierls state of ${\mathrm{CuGeO}}_{3}$ below 14 K has been determined by neutron-diffraction measurements. In addition to superlattice reflections with indices $\frac{h}{\frac{2kl}{2}}$ ($h$, $k$, $l$, all odd) recently observed in electron and x-ray diffraction studies, we also found peaks for which $k=5$ = even. Oxygen displacements in the $a\ensuremath{-}b$ plane of about 0.01 \AA{}, accompanied by comparable shifts of the Cu ions along the chain direction $c$, can be related to the dimerized spin state in a natural fashion.

We present results from a neutron-scattering study of lattice anomalies associated with the transition to the gapped spin-singlet state observed in the spin-1/2 linear-chain compound ${\mathrm{CuGeO}}_{3}$. Instead of the lattice dimerization along the chain direction (c axis) expected for a spin-Peierls system, we observe a remarkable softening of the longitudinal acoustic phonons in a direction (along the b axis) perpendicular to the chains. A spontaneous strain appears in the same direction below the magnetic transition temperature of 14 K.

Nd 1.85 Ce 0.15 CuO 4 single crystals of improved quality have been growth by the TSFZ method at an oxygen partial pressure in ambient atmosphere of 0.2, 0.1, 0.08 and 0.01 atm. Superconductivity in the as-grown state has been observed in the crystals grown at 0.08 and 0.01 atm. The improvement of the Ce distribution has been achieved due to a decreased value of the Ce distribution coefficient at low oxygen partial pressure in ambient atmosphere. The probability to obtain the same characteristics of the superconducting transition in the as-grown state as that in the crystals after post-growth high-temperature treatment seems to be very low because of oxidation during the cooling of the grown crystals from the crystallization temperature to room temperature.

Nd 2− x Ce x CuO 4 crystals have been grown by the TSFZ process at an oxygen partial pressure in the growth atmosphere of about 2.0, 0.2 and 0.1 atm. The corresponding values of the cerium effective distribution coefficient are 9.1, 3.4 and 2.4. It has been found that the Ce concentration in the central part of the crystals is slightly lower than that in the peripheral part, although the average Ce concentration has the same value as that in the feed rods. This phenomenon is discussed from the point of view of the different stirring conditions in the corresponding parts of the molten zone. The difference in the Ce concentration between the central and peripheral parts of the crystals becomes lower at decreased oxygen partial pressure in the growth atmosphere. Optimization of the growth conditions at the air atmosphere (oxygen partial pressure 0.2 atm) is pointed out as the promising way for quality improvement of the Nd 2− x Ce x CuO 4 single crystals.

Relations between the dopant contents in La2−xMxCuO4 (M=Ca, Sr, Ba) and the solvents of 78–80 mol% CuO and also the solubility of the dopants into La2CuO4 were investigated by the slow cooling floating zone method (SCFZ). The dopant content of La2−xMxCuO4 precipitated from the molten solvents increases as the dopant content of the solvents increases up to about 1.0. However, the contents of Ca and Sr in La2−xMxCuP4 are saturated at about 0.14 and 0.23, respectively, at a dopant content more than 1.0 in the solvents. The effective distribution coefficients k of the dopants into La2CuO4 are smaller than unity, and alson k becomes smaller in the order of Sr, Ca and Ba. kSr and kCa decrease with dopant content in La2−xMx CuO4 increasing, but kBa is about 0.13 which is independent on the Ba content in La2−xCuO4.

We have measured and calculated the electron-positron momentum distribution of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ samples for Sr concentrations of 0, 0.1, 0.13, and 0.2. Measured distributions were obtained at room temperature with high statistical precision, greater than 4\ifmmode\times\else\texttimes\fi{}${10}^{8}$ events, in the Lawrence Livermore National Laboratory positron-annihilation angular correlation spectrometer on single-crystal samples fabricated using the traveling solvent floating zone technique. Corresponding theoretical momentum-density calculations were performed using the linear muffin-tin-orbital method. The momentum distribution of all samples contained features derived from the overlap of the positron distribution with the valence electrons. In addition, discontinuities typical of a Fermi surface are seen in the doped samples. The form and position of these features are in general agreement with the Fermi surface and overall momentum distributions as predicted by band theory. However, the evolution of the Fermi surface with doping differed significantly from expectations based on single electron band theories.

We present the results of neutron-diffraction experiments on a series of La2−xSrxCuO4+δ single crystals at temperatures between 540 K and 22 K. There is an intrinsic misfit between the size of the LaO9 polyhedra and the CuO6 octahedra, which seems to cause the structural transition from the high-temperature tetragonal (HTT) to the low-temperature orthorhombic (LTO) phase. Within this misfit model it is possible to explain almost the entire phenomenology of the HTT-LTO transition. The electronic structure is related to this phase transition via the length of the CuO bonds. One of the effects of the transition on the structure is to lengthen these CuO bonds and hence to alter the electronic band structure. The introduction of additional charge by doping leads to a decrease of the equilibrium CuO distances, and hence to a reduction of the misfit. In this way the charge-carrier concentration determines the structural transition. We always observe strongly anisotropic thermal parameters, which confirm the instability of the La2−xSrxCuO4 structure against a rotation of the CuO6 octahedra around any axis. In the case of an undoped crystal (x = 0.0), we find a good agreement between the experimental mean square displacements and the results of a lattice dynamics model which is based on the known phonon dispersion curves. In a doped (x = 0.13) and superconducting crystal, the anharmonic effects related to the structural transition lead to significant changes in the temperature dependence of the thermal parameters.

Neutron-scattering experiments have been performed to study the dynamic spin properties of La{sub 1.85}Sr{sub 0.15}CuO{sub 4} ({ital T}{sub {ital c}}=33 K) in the temperature range 1.9 K{le}{ital T}{le}150 K and energy range 1.5 meV{le}{omega}{le}20 meV; these span, respectively, {ital T}{sub {ital c}} and the weak-coupling BCS gap energy 2{Delta}{similar_to}10 meV. The width of {ital S}({bold q},{omega}) in momentum space decreases with decreasing temperature at fixed energy as well as with decreasing energy at fixed {ital T}, becoming very sharp at both low {omega} and low temperature. It is found that both in the normal state at {ital T}=35 K and in the superconducting state at {ital T}=10 K the integrated generalized susceptibility {chi}{prime}{prime}({omega})={integral}{sub ({pi},{pi})} d{ital q}{sub 2D}{chi}{prime}{prime}({bold q},{omega}) is constant above {omega}{similar_to}10 meV with an amplitude about three times that in La{sub 1.98}Sr{sub 0.02}CuO{sub 4} and begins to decrease with decreasing {omega} at {omega}{similar_to}10 meV, which corresponds to the BCS superconducting gap energy 2{Delta}. However, we observe nonzero magnetic scattering well below the pseudogap energy at temperatures as low as 2 K. These results are compared with those in La{sub 1.98}Sr{sub 0.02}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub 6.6}.

The phase transition from the tetragonal to the orthorhombic structure in La2−x Sr x CuO4+δ has been studied combining elastic and inelastic neutron scattering and specific heat measurements on the same well characterized crystals. This analysis focusses on the comparison between undoped and doped compounds. The proportionality between the orderparameter and the orthorhombic strain, predicted by the Landau theory, can be confirmed in La2−x Sr x CuO4+δ in a wide concentration and temperature range. We observe different values for the critical exponent β for doped superconducting and undoped insulating crystals. The temperature dependent study of the soft modes on a metallic superconducting crystal reveals an extremely large temperature range where this mode is strongly anharmonic. The comparison with previously published data shows that the frequencies of the soft modes at low temperatures decrease with doping, i.e. with increasing charge carrier concentration.

The torque signal at fixed angle for fields up to 12 Tesla is measured in La1.85Sr0.15CuO in the fluctuation regime. The data are analysed using scaling theories in the high field limit.

A strong dependence of the cerium distribution coefficient ( K Ce ) on oxygen partial pressure P [O 2 ] has been shown in direct TSFZ experiments by changing the oxygen pressure during Nd 2−x Ce x CuO 4 single crystal growth. The ratio of K 0.1 atm Ce / K 0.2 atm Ce has been found to be equal to ∼0.62. Absolute values of K Ce measured from zone compositions have been found to be about 2.42, 3.37 and 9.06 at P[O 2 ]=0.1, 0.2 and 2.0 atm, respectively. Our experiment shows good agreement between measured and calculated K Ce values. We have shown that the quite large difference in K Ce obtained in a number of investigations is explained by a strong dependence of K Ce on P [O 2 ]. We have also shown that a reason for this dependence is the variable valence of Ce. Cerium effectively incorporates in a Nd 2−x Ce x CuO 4 single crystal in the form of Ce +4 ion.

We present a combined experimental and theoretical study of the effects of Sr doping on the electronic structure of La 2− x Sr x CuO 4 . Electron-positron momentum distributions have been measured to high statistical precision (> 4 × 10 8 counts) at room temperature for samples with Sr concentrations of x = 0.0, 0.1, 0.13 and 0.2. Analysis of all tour spectra reveal strong features due to electron-positron wavefunction overlap, in quantitative agreement with theoretical calculations. The Sr doped samples show discontinuities consistent with the presence of a Fermi surface. The form and position of these features are in general agreement with the predictions of band theory. Correspondence between theory and experiment, as well as some differences, are revealed by a detailed study of the changes in electron-positron momentum density with increasing Sr doping.

High-resolution ultrasonic measurements have been performed on single-crystalline ${\mathrm{La}}_{1.86}$${\mathrm{Sr}}_{0.14}$${\mathrm{CuO}}_{4}$ in magnetic fields H up to 14 T. We found that by reducing temperature the transverse elastic constant (${\mathit{C}}_{11}$-${\mathit{C}}_{12}$)/2 starts to soften from about 50 K and continues to soften down to ${\mathit{T}}_{\mathit{c}}$(H), even when ${\mathit{T}}_{\mathit{c}}$(H) is reduced to 14 K by magnetic field. The softening turns to rapid hardening by the emergence of superconductivity. This behavior of C${(}_{11}$-${\mathit{C}}_{12}$)/2 is a consequence of the structural instability of the orthorhombic phase and disappearance of the instability caused by emergence of the superconducting state.

Capacitance-dilatometer measurements of the anisotropic thermal expansion on a superconducting single crystal of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ (x\ensuremath{\sim}0.13) show large anomalies at the structural transition from the high-temperature tetragonal to the low-temperature orthorhombic phase followed by smaller anomalies of the opposite sign at the superconducting phase transition. Neutron-diffraction experiments on the same crystal indicate that at ${\mathit{T}}_{\mathit{c}}$ the tilt of the ${\mathrm{CuO}}_{6}$ octahedra related to the structural phase transition is frozen in.

It was found that NdAlO 3 has a reversible phase transition at a temperature close to its melting point. Substitution of Y for Nd in NdAlO 3 was effective in stabilizing the high temperature phase. Crystals of Nd 1-x Y x AlO 3 (0≤x≤0.25) were grown by the floating zone (FZ) method using an infrared furnace. The crystals had some cracks, subgrain boundaries and domain structure, and 'also were not uniform in Y concentration due to supercooling

Neutron scattering experiments have been performed to study the dynamic spin properties of single-crystal La 1.86 Sr 0.14 Cu 0.988 Zn 0.012 O 4 ( T C =16 K). The width of S ( Q , ω) in momentum space decreases at low ω and at low temperatures. The intensity at low energies at the incommensurate peak position (π(1-δ), π)) shows a broad maximum as a function of temperature around the superconducting transition temperature T C . This behavior is qualitatively similar to that observed by Thurston et al . in La 1.85 Sr 0.15 CuO 4 ( T C =33 K).

The positive muon (μ+) spin relaxation method under zero external field is applied to probe magnetic ordering in the superconducting phase of a high quality single crystal of La2−xSrxCuO4 (0.10

The negative muon (μ−) was used as a microscopic probe for the study of the electronic state at the oxygen site in highTc related LaSrCuO materials. Using good single crystals, two types of signals are obtained corresponding to two different oxygen sites: one highly anisotropic, which shows a large (order of 1%) shift under the magnetic field inc-axis direction, the other less anisotropic and with a smaller amplitude (order of 0.2%). These results of μ−OSR show quit a difference with the result of17O-NMR, where the paramagnetic shift has axial symmetry along the Cu-O bond direction and a magnitude of the order of 0.2% and 0.05%.

In order to investigate the electronic structure around oxygen in superconducting La2−x Sr x CuO4 (x=0.10 and 0.14), precise measurements were carried out on the paramagnetic Knight shifts in the spin rotation frequency of the negative muon bound to the oxygen with reference to antiferromagnetic La2−x Sr x CuO4 (x=0.05). Remarkable temperature as well as crystalline-axis dependence was observed for the highT c case with a divergence character towardsT c. Possible mechanisms to explain the observed results are given.

By using a monodomain single crystal La2CuO4 grown by the travelling solvent floating zone method, the strength and direction of the local hyperfine field vector at positive muon sites were determined. Combining with the μ+ location determined separately, we found the importance of the local hyperfine field contributions with dipolar symmetry as well as the distant dipolar field from surrounding point dipoles of Cu atomic moments.

Neutron-scattering experiments with markedly improved signal-to-noise ratios have been performed on single-crystal superconducting La[sub 1.85]Sr[sub 0.15]CuO[sub 4] ([ital T][sub [ital c]]=33 K) at energies down to 1.5 meV. The measurements provide quantitative information on the temperature dependence of [chi][prime][prime]([bold q],[omega]). Surprisingly, [chi][prime][prime]([bold q][sub peak],[omega]) is approximately constant below [ital T][sub [ital c]] for the measured energies 1.5 meV[le][omega][le]6 meV, that is, for energies much less than the mean-field BCS gap energy of [similar to]10 meV, hence implying other than conventional [ital s]-wave superconductivity.

Measurements are reported of the static, instantaneous, and dynamic spin correlations in single crystals of ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4+\mathrm{\ensuremath{\delta}}}$. The as-grown crystals show antiferromagnetic long-range order. However, the N\'eel temperatures and spin-stiffness constants are greatly reduced from their respective values in ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4+\mathrm{\ensuremath{\delta}}}$. After reduction and annealing, the crystals superconduct with ${\mathit{T}}_{\mathit{c}}$=23 K, but inclusions of the antiferromagnetic phase, albeit with reduced N\'eel temperatures, are always present. Based on these data, we suggest that the disorder due to excess oxygen in as-grown samples stabilizes the magnetic correlations. This leads to a speculative model for the effects of deoxygenation in which the removal of the excess oxygen causes the magnetic correlations to diminish and hence superconductivity to become possible.

We have measured the magnetic susceptibility and the anisotropy for a (La1-xSrx)2CuO4 (x=0.075) single crystal in the fluctuation regime for fields between 0 and 5 T. The fluctuation contribution close to Tc is smaller than the one expected from standard 3D or 2D Ginzburg-Landau theory. Our data could be rescaled according to the model proposed by Ullah and Dorsey, using 2D exponents. The anisotropy data shows a deviation from linearity in the vicinity of Tc, for fields close to the plane direction, which we attribute to the onset of bulk superconductivity.

The infrared (IR) reflection spectra were measured on single crystals of La 2− x Sr x CuO 4− δ ( x =0, 0.09, 0.14 and 0.19) by using specially made far-IR and IR microspectrophotometers. The spectra show the Drude, the phonon and the mid-IR exciton bands. The near-IR to UV reflection spectra were also measured. The dielectric functions were calculated by Kramers-Kronig transformation of the reflection spectra. The plasma frequency of the Drude band is relatively small (4100 cm −1 for x =0.14). We found all predicted phonon bands and several other phonon bands which appeared by the lowering of the D 4h symmetry of the CuO 4 cluster. We confirmed the presence of the mid-IR exciton bands and the 1.7 eV band which appeared by the doping and assigned them to the transition from the deeply lying O 2p energy bands to the hole in the uppermost O 2p energy band. The mid-IR exciton bands show an anomalously strong intensity, which comes from the coupling of the exciton and the charge fluctuation of the electron.

Magnetization curves of large single crystals of (La1-xSrx)2CuO4 (x=0.065 and 0.07) were measured at temperatures from 4.2 to 30K under magnetic fields of up to 9T. The crystals utilized had long dimensions in either the c-axis or the a-axis direction along which the magnetic field was applied, in order to minimize the demagnetization effect. The analysis of the hysteresis data revealed strong anisotropy in flux pinning and critical current density, Jcab(H//c), Jcab (H//ab) and Jcc (H//ab). It was found that the field and temperature dependence was most pronounced for Jcab(H//c) and discussion will be made for this particular case in terms of the conventional scaling law.