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Flux jumps have been observed in a large (138 mg) single crystal of La 1.86 Sr 0.14 CuO 4 . Both complete and incomplete flux jumps are observed with the energy dissipated by complete flux jumps consistent with temperature rises to nearly T c . The systematics of these flux jumps with respect to field history, temperature and the time duration of the hysteresis measurements are reported. The field at which flux jumps first occur and their subsequent spacing are not consistent with a simple adiabatic theory of flux jumps for our experimental conditions. Instead, the crystal is observed to be stabilized against flux jumps by flux creep which occurs during the time interval over which field steps are accomplished as well as during imposed time intervals between field steps.

The ionic-electronic conducting compounds of lithium vanadium bronzes, copper vanadium bronzes, and Mo doped vanadium bronzes were obtained from molten LiVO 3 − V 2 O 5 system, V 2 O 5 − Li 3 PO 4 system, V 2 O 5 − CuCl system, and V 2 O 5 − Li 2 MoO 4 system by electrolysis. The electrolysis conditions were determined from the cyclic voltammograms of electrolytic bath at 650°C to 800°C. The mixture melts of V 2 O 5 containing 9.1 mol% Li 3 PO 4 were used as the ideal composition of electrolytic bath for β-Li z0.36 V 2 O 5 crystallization. The lithium contents of β-Li 0.36 V 2 O 5 cystals were controlled with current density and composition of electrolytic bath. The crystals of Li 0.29 V 1.82 Mo 0.18 O were obtained from electrolysis of V 2 O 5 melts containing 25 mole% Li 2 MoO 4 . The activation energy of conductivity for Mo doped lithium vanadium bronzes was less than the non Mo doped bronzes.

Magnetic relaxation and hysteresis studies have been performed for a c-axis-oriented single crystal of ${\mathrm{La}}_{1.86}$${\mathrm{Sr}}_{0.14}$${\mathrm{CuO}}_{4}$. We demonstrate that the effective activation energy for flux creep, ${\mathit{U}}_{\mathrm{eff}}$, is a strongly nonlinear function of the current density J (as given by the irreversible magnetization). For fixed fields of 0.5, 1.0, 2.0, and 3.0 T and temperatures between 4 and 15 K (as consistent with full field penetration of the sample), ${\mathit{U}}_{\mathrm{eff}}$(J) is seen to vary approximately logarithmically with J. A scaling relationship, ${\mathit{U}}_{\mathrm{eff}}$(J)=[-${\mathit{U}}_{1}$g(T)/${\mathit{H}}^{\mathit{n}}$]ln(J/${\mathit{J}}_{\mathit{c}}$), is shown to be obeyed for this crystal with n\ensuremath{\simeq}0.9 (H in T), ${\mathit{U}}_{1}$\ensuremath{\simeq}180${\mathit{k}}_{\mathit{B}}$, and ${\mathit{J}}_{\mathit{c}}$(1 T)\ensuremath{\simeq}3.2\ifmmode\times\else\texttimes\fi{}${10}^{5}$ A/${\mathrm{cm}}^{2}$. Several functional forms of g(T) have been explored and shown to give reasonable fits if monotonically decreasing in temperature over the range where flux creep is observed. We also explore the ramifications of this functional dependence in explaining an observed exponential temperature dependence of the hysterically determined critical current density. Finally, we show that comparison of the temperature dependence of logarithmic relaxation rate A=dM/d ln(t) and the derivative of the magnetization with respect to ln(T) at fixed time, ${\mathit{dM}}_{0}$/d ln(T), can be used to set a scale of the attempt frequency for flux motion consistent with the other measurements.

The torque signal near T c was studied on a (La 1− x Sr x ) 2 CuO 4 ( x =0.075) single crystal. For fields applied close to the plane direction, the reversible torque signal could be fitted with the anisotropic London theory using an anisotropy ratio γ( T )=10 to 20, (d(1/λ 2 )/d T ) T c ≈2.7 μm -2 K -1 and (d(η H c2· )/d T ) T c ≈2T K -1 . The signal exhibits irreversibility associated with the trapping of flux lines between the superconducting planes. The magnitude of the effect decays exponentially with temperature and field.

The positive muon spin relaxation method is applied to probe magnetic ordering in the superconducting phase of a high quality single crystal of La2−xSrxCuO4−σ (0.11≤x≤0.14). The well characterized crystal ofx=0.11 (T c=34.5 K) with nearly complete flux exclusion exhibits spin freezing at 8K(T f) with significant spin fluctuation up to 20 K. The onset of spin fluctuation andT f decrease against increasingx towardsx=0.15, suggesting an existence of a magnetic phase boundary aroundx whereT c becomes maximum.

A novel microscopic method of muon spin rotation for negative muon (μ−) attached to oxygen is applied on highTc materials LaSrCuO. The paramagnetic shift and relaxation rate are measured as a function of Sr concentration and temperature. Analysis shows the large difference in shift and relaxation between two different sites. A large anisotropy was also observed by preliminary measurements along different crystalline axes.

In order to elucidate whether the superconductivity of the cuprate HTSC is 'normal' or 'abnormal', systematic studies have been performed on the Meissner effect, lower and higher critical fields. The Meissner fraction is strongly dependent on the size of sample and on the field, which is explained by a novel model considering the sharp increase in the vortex pinning force while the flux expulsion process proceeds as T is lowered. Another new method has been proposed to determine Hc1 from the magnetization curve above Hc1, based on which the abrupt upturn of the Hc1-T curve frequently reported in the low T region has been attributed to the error induced by the strong pinning. The ambiguity associated with the Hc2-T curve is discussed in terms of the 'giant fluctuation' of superconductivity.

Linewidths of some transverse acoustic phonons have been studied as a function of temperature on a superconducting single-crystal sample of ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$ (${\mathit{T}}_{\mathit{c}}$=33 K) with the goal of measuring the electron-phonon interaction. The phonons studied have energies in the range \ensuremath{\omega}\ensuremath{\sim}6.0--9.5 meV and observed full widths at half-maximum in the range 2${\ensuremath{\gamma}}_{\mathrm{obs}}$\ensuremath{\sim}0.25--0.5 meV. No temperature-dependent changes were observed in any of the linewidths near the transition temperature. This null result is consistent with a low electronic density of states at the Fermi surface, and an electron-phonon coupling parameter \ensuremath{\lambda} that is not unusually high compared with conventional superconductors.

Phase diagrams of the Nd2O3-CuO and (Nd. Ce)2O3-CuO systems were investigated by differential thermal analysis. It was found that Nd2CuO4 and Nd2-xCexCuO4 melt incongruently at 1270±5 °C and 1315±5 °C respectively, and the solids of Nd2CuO4 and Nd2-xCexCuO4 exist in equilibrium with the liquid of 79–91 mol% CuO, respectively. On the base of these results, Nd1.86Ce0.14CuO4 single crystals were grown by the traveling solvent, floating zone (TSFZ) method. The as-grown crystals were 5 mm in diameter and 50 mm in length with a lusterless black, and had a few subgrains. The Meissner signal was not observed from the as-grown crystals, but it was observed below 19 K from the crystals annealed in N2 at 900 °C for 70 hours.

A novel resonant ultrasound technique is used to measure all elastic constants and their temperature dependence in single-crystal La{sub 1.86}Sr{sub 0.14}CuO{sub 4}. The in-plane shear modulus {ital c}{sub 66} drops by nearly half upon cooling to 227 K, an effect attributed to order-parameter fluctuations (of 2D Gaussian character) near the tetragonal-orthorhombic phase boundary. Implications for current models of the structural phase transition are discussed, as well as the effect of domains in the low-temperature orthorhombic state.

The anisotropic lower critical fields ${\mathit{H}}_{\mathit{c}1}$ are determined from a novel procedure based on the Bean's critical-state model to pick up the onset of flux penetration in broad zero-field-cooled magnetization curves in (${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${)}_{2}$${\mathrm{CuO}}_{4}$ (x\ensuremath{\approxeq}0.07) single crystals. The values of ${\mathit{H}}_{\mathit{c}1}$ at T=0 K are estimated to be 70 G for H\ensuremath{\parallel} layer and 300 G for H\ensuremath{\perp} layer. The temperature dependence of ${\mathit{H}}_{\mathit{c}1}$ is such that it tends to saturate towards the lowest temperature measured (2 K) in contrast to the other recent results which report the abnormal upturn of the ${\mathit{H}}_{\mathit{c}1}$-T curve at low temperatures. Instead the results indicate that the critical current density in plane has a strong temperature dependence even in the temperature range well below ${\mathit{T}}_{\mathit{c}}$ and becomes \ensuremath{\sim}${10}^{6}$ A/${\mathrm{cm}}^{2}$ at 2 K.

Single crystals of beryl grown by slow cooling from an impurity doped flux without a seed crystal have been grown and their habit modifications studied by SEM and optical microscopic observation. Transition metal doping using Fe 2 O 3 , Cr 2 O 3 , Mn 2 O 3 and alkali metal doping experiments were also carried out. Two characteristics, (1) the ratio (H/W), height to width of the crystals and (2) combination and relative development of crystal faces, were used as a measure of habit modifications. In general, as impurity doping increased, the crystals became slender and the second order prism disappeared. The ratio H/W was less in the larger crystals. This tendency can be attributed to the selective incorporation of impurity atoms on certain faces.

Single crystals of SrTa 2 0 6 and Ba 0.1 Sr 0.9 Ta 2 O 6 were grown by the floating zone method using an infrared heated furnace. The grown crystals of SrTa 2 0 6 and Ba 0.1 Sr 0.9 Ta 2 O 6 were about 5 mm in diameter and up to 35 mm long. The crystals of SrTa 2 O 6 showed a transition from the tetragonal structure to the orthorhombic structure at about 600 °C, whereas the crystals of Ba 0.1 Sr 0.9 Ta 2 O 6 exhibited the tetragonal structure without a phase transition. The dielectric constants ∈ of the SrTa 2 O 6 single crystals were independent of frequency and anisotropic with ∈ α =108 and ∈ c =128. However, ∈ c decreased as frequency increased for the Ba substituted crystals.

Sharp quasi-elastic peaks ( κ = 0.014 A −1 , Λ = 0.22 meV ) indicating long-range antiferromagnetic slow fluctuations, were observed at (π,π) + e(π,0) in La1.86Sr0.14Cu0.988Zn0.012O4−δ in superconducting (δ = 0, Tc = 19 K) and non-superconducting (δ = 0.0040) conditions. The quasi-elastic components start appearing around Tc and increase with lowering temperature, while the low-energy inelastic peaks with the same e show a broad intensity maximum around the same temperature.

We measured Raman scattering below 400 cm−1 in Cu1−xZnxGeO3 (x = 0, 0.013, 0.017, and 0.0212) to study the Zn-doping effect in the spin-Peierls phase. When Zn atoms (S = 0) are doped, a two-magnetic-exciton bound state disappears in the spin-Peierls phase. In the sample of x = 0.0212, the folded phonon mode at 370 cm−1 and the two-magnetic-exciton Raman spectra below 250 cm−1 were observed even in the uniform phase. In pure CuGeO3, the quasi-elastic scattering was observed at high temperatures. The origin of this scattering is considered as a spin fluctuation interacting with lattice.

The flux line lattice (FLL) elasticity and its anisotropic pinning have been investigated in a single crystalline La 1.85 Sr 0.15 CuO 4 by ultrasonic measurements under high magnetic fields. The depinning activation energies are deduced from measurements under various settings of the directions of wave vector k, polarization vector u and magnetic fields H as U ac (0 K, 14 T) = 972 K for H⊥ c, uc. U ab (0 K, 14 T) = 201 K for H⊥ c, uc × H) and U ca (0 K, 14T) = 25K for Hc, u⊥c. The magnetic field dependence of U are also deduced as U ac ∝ H −0.3 and U ca ∝ H −1.5 . The angular dependence of U ac is discussed on the basis of the intrinsic pinning mechanism.

We have measured two phonon-dispersion curves above 50 meV in a superconducting (T c = 33 K) single crystal of La 1.85 Sr 0.15 CuO 4 . In the normal phase (T = 45 K), we show that the Λ 1 mode compatible with the Raman A 1g (425 cm -1 ) mode is weakly dispersive, falling from 53.7 meV at the zone center to about 51 meV at the zone boundary along the tetragonal (0,0,ξ) direction. For the Λ 1 mode compatible with the infra-red A 2u (480 cm -1 ) mode, we observe a significant dispersion of the phonon energy which drops monotonically from 60 to 56 meV. The global features of these dispersion curves are similar to those previously reported in studies of both pure and 10% Sr doped La 2 CuO 4 . However significant differences in the shape of the dispersion of the highest Λ 1 branch is shown, as well as a significant softening with increasing carrier concentration.

Faraday rotation in CuGeO3 was measured in magnetic field, up to 500 T produced by means of electromagnetic flux compression. The magnetization deduced from the rotation angle showed a distinct saturation around 250 T, and the exchange parameter was evaluated as 183 K from the saturation field based on the uniform Heisenberg chain model.

Novel softening has been found in the transverse elastic constant (C 11–C 12)/2 below 50 K in single-crystalline La1.86Sr0.14CuO4 (LSCO) by high-precision ultrasonic measurements in magnetic fieldsH along thec axis. With decreasing temperature, this lattice softening persists down to the superconducting transition temperatureT c(H), which is reduced to 14 K by applying fields up to 14 T. BelowT c(H) the softening turns to rapid hardening. This behavior indicates the presence of lattice instability of the orthorhombic (Bmab) structure in the normal state of LSCO, which disappears in the superconducting state. This is evidence for the intimate interplay between high-T c superconductivity and the lattice instability in LSCO.

Pyrochlore type Na0.39Bi3.47O7 containing Bi5+ was prepared by low temperature hydrothermal reaction using hydrated sodium bismuth oxide, NaBiO3⋅nH2O, as a starting material. The mean valence of Bi in the pyrochlore is 3.94. The X-ray powder pattern for the pyrochlore was indexed in the cubic system with a=10.943(8)A. The crystal structure was refined with the X-ray powder Rietveld method. The final R-factors, RWP, RP and RB were 13.3, 9.5 and 12.8%, respectively. The pyrochlore decomposes above 380°C with two steps of weight losses caused by complete reduction from Bi5+ to Bi3+. The Na-pyrochlore exhibited high electric resistivity (-107Ω⋅cm) at room temperature.

Surface of La2CuO4 single crystals were oxidized by KMnO4 aqueous solutions. The oxidation conditions such as KMnO4 concentration, soaking time and solution temperature of KMnO4, were systematically controlled. The magnetic properties of the crystals were drastically dependent on the oxidation conditions. The superconducting transition properties under the optimum condition, 48 h, 150°C and 5 wt%, were T c = 28 K and ∆T c = 2K. The chemical oxidation was limited only to the surface region of the crystals. Therefore, chemical oxidation may be useful for the preparation of superconducting single-crystalline films.

La2-xBaxCuO4 (LBCO) single crystals were grown under oxygen partial pressure (Po2) of 1~200 kPa by the traveling solvent floating zone (TSFZ) method. The Ba solubility in the LBCO crystals was maximum for growth under about 100 kPa, and was decreased with deviating Po2 from 100 kPa. The Ba solubility in the LBCO grown crystals was increased up to 0.19 under 100 kPa, but the grown crystals contained subgrains and inclusions of La4BaCu5O13 and CuO. The subgrain- and inclusion- free single crystals of LBCO with the Ba concentration x≤0.113, the typical size of 5 mm in diameter and 30 mm in length, were obtained under 100 kPa.

Precision lattice parameter in La1.85Sr0.15CuO4 single crystal superconductor has been measured in a wide temperature range between 4.2 K and room temperature by the X-ray Bond’s method. An anomalous lattice contraction associated with the appearance of the superconductivity was found in c-plane. Along c-direction, on the contrary, an anomalous expansion of the lattice was observed. The relative spontaneous change in the lattice parameter in c-plane was 2.3xl0­-5 and that of c-axis was 1.5×l0-5 at 4.2 K. The temperature dependence of the spontaneous lattice change was compared with currently existing theories for high Tc superconductivity.

We report normal-state electrical resistivity of La2-xBaxCuO4-δ single crystals with x=0.06, 0.08 and 0.09, grown by TSFZ method. The resistivity is non-metallic both in ab-plane and along c-axis in as-grown crystals. In-plane metallic resistivity evolved by annealing in oxygen. This result indicates the oxygen deficiency in as-grown crystals. The perturbation of the CuO2 sheet potentials due to oxygen-vacancies in the crystal lattice possibly induces semiconducting behavior in as-grown crystals. Filling the vacancies by annealing in oxygen relieve the perturbation of the sheet potentials, results in metallic resistivity in the ab-plane. A good fit of the experimental data found with RVB model.

By measuring the ultrasound velocity for various modes, we found unusual temperature dependence of the elastic coefficients in single-crystalline La2−xSr x CuO4 with x = 0.09, 0.14 and 0.19. The longitudinal elastic coefficients show a rapid drop in La2−xSr x CuO4 at Tc, as is seen in conventional superconductors. As the temperature decreases, however, the lattice shows gradual hardening in La2−xSr x CuO4 both for the longitudinal and transverse modes of ultrasound in contrast to most of the conventional superconductors, in which the lattice continues to soften in the superconducting state. According to thermodynamic analysis, the temperature dependence of the elastic coefficients below Tc suggests that the second strain derivative of the superconducting condensation energy d2 O /d e 2 is negative in La2−xSr x CuO4, whereas the sign is positive in the conventional superconductors. An important possibility is that this unusual lattice hardening in the superconducting state is a common character of the high-Tc copper oxides.

We report the results of an x-ray-scattering study of the [ital b]-axis lattice constant of the quasi-one-dimensional spin-1/2 antiferromagnetic chain system CuGeO[sub 3] as a function of temperature and magnetic field. A spontaneous thermal contraction [Delta][ital b] along the [ital b] axis perpendicular to the chain direction is observed below the spin-Peierls transition temperature [ital T][sub [ital c]] near 14 K. The contraction, [Delta][ital b], is well described by a simple power law, [Delta][ital b][proportional to](1[minus][ital T]/[ital T][sub [ital c]])[sup [ital x]], where the exponent [ital x] is found to be close to 0.5. Below the transition temperature, [Delta][ital b] scales with the intensity of the superlattice reflections with indices ([ital h]/2,[ital k],[ital l]/2)([ital h],[ital l]: odd, [ital k]: nonzero integer) measured by neutron scattering. The shift of the transition temperature, [Delta][ital T][sub [ital c]][equivalent to][ital T][sub [ital c]](0)[minus][ital T][sub [ital c]]([ital H]), is found to scale as [ital H][sup 2] in quantitative agreement with the results of magnetic susceptibility measurements and with theory. A small increase in the [ital a]-axis lattice constant is observed below [ital T][sub [ital c]].

Phase relations between La2-xSrxCuO4 solidus and liquidus were determined by TG-DTA and a slow-cooling experiment. Single crystals of high Sr-doped La2-xSrxCuO4 (x>0.15) were grown by the TSFZ method on the basis of the phase relations. The grown crystals, 5 mm in diameter and about 30 mm in length, were crack-free and black with a metallic luster. The grown crystals of x=0.20 had no inclusions and subgrains. However, the grown crystals of x=0.25 contained subgrains, and those of x=0.30 had inclusions of La2-xSr1+xCu2O6+δ.

We studied the superconducting properties of an electron irradiated La1.85Sr0.15CuO4 single crystal. Point-like defects are introduced into the crystal with the irradiation. The irradiation decreases the correlation between CuO2 layers. However, both before and after the irradiation, the flux creep activation energy Ueff (J,T,H) can be expressed the same formula as Ueff (J,T,H) = const.*In(J)*(1-T/Tc)n/H, where n is a constant determined from the irreversibility line.

Bulks of YBCO superconductor were prepared by melt process with seeding single grains of YBCO and SmBCO superconductors and single crystals of SrTiO3 and MgO. The seedeing of YBCO single grain and MgO single crystal was effective for the growth of single-grained bulk of YBCO superconductor. The maximum size of the single-grained YBCO bulk was 45 mm in diameter and 15 mm in thickness.

In order to estimate the magnetic shielding effect of YBCO bulk at macroscale, spatial distribution of magnetic field was measured with a Holl-probe. The shielding effect of zero field cooled sample was measured under magnetic fields (0.5,1,2 kOe). Crystallographic analysis were carried out by Laue method and optical microscope. The YBCO bulk prepared by MMTG method has domain structure. Both low-angle (misorientation of 10°) grain boundaries among macrograins (~cm) are observed. Our experimental results show that high-angle grain boundaries make week link and hence magnetic flux invades along this boundaries.

La2CuO4 single crystals grown at an oxygen pressure of 0.2 MPa by TSFZ method are superconducting below 32 K, and show a semiconducting behavior in nonsuperconducting state. The single crystals of La2Cu04 are changed from superconductors to semiconductors by annealing in argon, and are returned to superconductors by annealing at ambient pressure of oxygen. Therefore, superconductivity of the La2CuO4 single crystals is due to excess oxygen.

Magnetic susceptibility of superconducting single-crystal La2−x Sr x:CuO4 (x = 0.12, 0.14 and 0.19) was measured with a SQUID magnetometer from 30 to 300 K under the magnetic fields (H) of 1 ~ 5 T. The field- dependent susceptibility is evident below 40 K under H perpendicular to the CuO2 planes and is assigned to the superconducting fluctuation-induced diamagnetism (SFD). The field-independent part was subtracted by taking the difference of the susceptibilities for the different H. The field-dependent part was fitted by using the two-dimensional form of the Lawrence-Doniach model for SFD. The magnetic-field dependence of the superconducting-transition temperature was obtained by this analysis. The values of the in-plane coherence length at 0 K are determined as 28.3, 29.2 and 32.5 A for the samples of x = 0.12, 0.14 and 0.19, respectively.

Tunneling spectroscopy studies have been performed on differently doped la 2−x Sr x CuO 4−δ single crystals by break junction technique. By a fine adjustment of the mechanically controlled spacing between the two fractured electrodes, we were able to investigate highly stable conductance characteristics along the ab -planes in various tunneling regimes. In the weak link regime, Josephson effect was clearly observed with critical current decreasing monotonically with temperature and vanishing below the crystal's T c . By increasing the electrode's distance, in the quasiparticle regime, a well developed zero bias conductance peak and smeared gap-like structures were observed. All these features are consistent with the d-wave model for high T c superconductors.

We observed a multi-branch behavior in the flux-flow branch of current–voltage characteristics of stacks fabricated along the c axis in La2−xSrxCuO4 single crystals. The voltage increases with increasing an external magnetic field applied parallel to the ab plane. The multi-branch behavior may originate from a chaotic motion of Josephson vortices with many velocity modes.

We studied La 1.85 Sr 0.15 CuO 4− δ single crystals by tunneling spectroscopy both in planar and in break junction configurations. In the c -axis oriented planar junctions, with natural barriers and evaporated Pb film counterelectrodes, we observed at low-temperature gap-like structures around ±7–10 meV. In the a , b oriented break junctions we found conductance structures at ±15–20 mV, an increasing background at high biases and a conductance peak at zero voltage. The presence of this peak can be interpreted in terms of d-wave component for the order parameter in this material.

Magnetization curves of (La1−xSrx)2CuO4 (x=0.065−0.07) single crystals were measured at temperatures from 4.2 to 35K under magnetic field of up to 9T. The field was applied along the a- or the c-axis of the two types of the crystals having different macroscopic geometry. The analysis of the hysteresis data revealed strong anisotropy in flux pinning and critical current density. At 4.2 K and 5 T, for example, Jc//ab-plane(H//c-axis), Jcc(H//ab) were determined to be 2.1×105, and 3.0×104 A/cm2, respectively and Jcab(H//ab) was estimated to be 4.2×105 A/cm2. It was also found that the field and temperature dependence was quite appreciable in Jc//ab(H//c), as expected from the generally observed behavior in cuprate-based HTSC oxides.

Single crystals of La2CuO4 5 mm in diameter and 50 mm in length were grown at an oxygen pressure of 0.2 MPa by the traveling solvent floating zone method (TSFZ method). The as-grown crystals of La2CuO4 were superconducting, but were a mixture of a superconducting phase and an antiferromagnetic phase. The single crystals of La2CuO4 were changed reversibly from superconductors to nonsuperconductors by annealing. In the nonsuperconducting state, the single crystals of La2CuO4 were semiconducting and had a highly anisotropic resistivity, where the resistivity ratio ρ ⊥/ρ ‖ was about 28,000 at RT.

Using a transverse vibrating sample magnetometer, we have made vector magnetisation measurements on a disk-shaped single crystal La1.9Sr0.1CuO4. Reversible behaviour of the c-axis component of magnetisation, and the angular dependences of the remanent moment are evidence of the vortex lock-in state. The lock-in angle dependence on temperature and applied magnetic field are in agreement with theory.

Superconducting single crystals of La 2- x Sr x CuO 4-δ ( x = 0.15 and 0.20) were studied by means of the vector magnetization technique. The effective mass anisotropy factors are estimated to be Γ = 100 and Γ = 2, respectively, for the two samples. A procedure is proposed to obtain the thermodynamic orientation of the flux line lattice from the irreversible magnetization. Direct evidence is reported of vortex penetration along the easy plane. The data agree with numerical results for a three-dimensional anisotropic superconductor.

Linear Cu2+ (S = 12) inorganic chain compound CuGeO3 exhibits a spin-Peierls (SP) transition at 14 K. The present report describes the existence of the strong fluctuation and/or the formation of short-range order above 80 K associated with the appearance of the satellite reflection with h/2 k 32 (h:odd, k:integer). It may lead to the explanation of the difference between the χ(T) and the Bonner-Fisher law. The temperature dependence of the b lattice constant and the integral breadth at 040 reflection is consistent with the observation of the softening of the LA phonons along the b axis and the spontaneous strain Δb by Lorenzo et al.

Ultrasonic measurements were performed on single crystals of La 2− x Sr x CuO 4 (LSCO) with x = 0.09, 0.14 and 0.19. We found that the elastic constants of LSCO increase well below the superconducting transition temperature T c , in contrast with softeniing observed in conventional superconductors. The difference originates from the change in superconducting condensation energy o under the lattice strain e i induced by a sound wave.

We present high-resolution dilatometry measurements of a La 1.87 Sr 0.13 CuO 4 -single crystal parallel and perpendicular to the CuO 2 -planes in magnetic fields up to 14 Tesla. We find a strong suppression of the thermal expansion anomalies for magnetic fields parallel to the c-axis. In contrast, a magnetic field perpendicular to the c-axis affects the anomalies only weakly.

Nd 1.85 Ce 0.15 CuO 4 single crystals of improved quality were grown by TSFZ method at low oxygen partial pressure of 0.2, 0.1, 0.08 and 0.01 atm. Superconductivity in as-grown state was observed in the crystals grown at 0.08 and 0.01 atm. The improvement of Ce distribution was achieved due to decreased value of Ce distribution coefficient at low oxygen partial pressure in ambient atmosphere. The probability to obtain the same characteristics of the superconducting transition in 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 the room temperature.

High-precision ultrasonic measurements of sound velocity and attenuation in magnetic fields up to 14 Tesla were carried out on a single-crystalline La 2-x Sr x CuO 4 with x =0.1, 0.14 and 0.19 to determine the depinning temperature of the flux lines as functions of doping. With decreasing Sr-content the depinning temperature, determined by the midpoint of the step in the sound velocity, decreases strongly. Furthermore, the angle dependence of the tilt modulus of the flux line lattice was studied by changing the orientation of the magnetic field with respect to the k-vector and to the displacement vector of the sound wave.

An increase of the sound velocity reflecting the elastic constant of the flux line lattice and its pinning are observed in the mixed states of a La1.85Sr0.15CuO4 single crystal. Each anisotropic activation energy which is necessary to depin the flux line lattice is evaluated independently from measurements under various settings of the wave vector k , the polarization vector u and magnetic fields H using the analysis based on the thermally assisted flux flow model. It is found that the activation energy in the case of H ⊥ c -axis and u | c -axis is extremely higher than others. This result suggests the importance of the intrinsic pinning mechanism due to the layer structure.

We compared superconducting properties of a La1.85Sr0.15CuO4 single crystal between before and after electron irradiation. About 100 ppm point-like defects are introduced into the crystal with the irradiation. Both irreversibility lines and hysteries measurements indicate that the irradiation decreases the superconducting currents flowing between CuO2 layers. The flux creep activation energy UeffJ) is proportional to g(T)1n(J), where g ( T )=(1- T / Tc ) n .

Ultrasonic and specific-heat measurements have been performed across the superconducting transition on a single crystal of La1.86Sr0.14CuO4. A pronounced jump of the elastic constant ΔC33(Tc) = -0.15 GPa is observed at Tc = 34 K as well as a specific-heat jump Δcp/Tc = 9.6 mJ/K2mol, whereas a jump in C11 is less obvious. The results allow quantitative estimation of the strain dependence of Tc and the condensation energy along the a and c axes.

Temperature dependence of the sound velocity V s in a La 1.85 Sr 0.15 CuO 4 single crystal has been measured in the ( c 11 − c 12 )/2 mode and in the c 33 mode under high magnetic fields up to 23T. In the field above 6T, V s in the ( c 11 − c 12 )/2 mode anomalously decreases with decreasing temperature, followed by the increase below about 10K. In the c 33 mode, similar behavior of V s can be observed above 20T. Such a temperature dependence of V s may suggest the existence of a strain sensitive narrow band near the Fermi level or a phase transition related to the flux line lattice.