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This study discusses the conditions for the occurrence of two-dimensional superconductivity under the action of an electric field on an La2 – xSrxCuO4 plate at a temperature lower than the maximum temperature of the superconducting transition, but when the concentration of charge carriers falls outside the superconductivity range. The study is carried out for a lanthanum-strontium cuprate plate at various hole concentrations, as well as temperature, and potential differences. A quasi-two-dimensional superconducting layer arises near the surface of the plate. The thickness of the superconducting layer is several angstroms and independent of the field strength in the range investigated. The thickness depends only on the concentration of holes and temperature. In addition, the distance of the superconducting layer from the edge of the plate is found to be a function of all three factors. The conditions used for conducting the experiment are also formulated. [ABSTRACT FROM AUTHOR]

This study presents synthesis results of catalysts made of perovskite-like oxide La2-xSrxCuO4 (x=0.0, 0.5, 1.0) using the citrate method and crystallisation at 800°C. The structure of the catalysts was characterised by X-ray diffraction (XRD). The perovskite- like oxide catalyst activity was enhanced with gold (Au) and platinum (Pt). Au was mounted on the perovskite-like oxide catalysts by the sol-gel method. The activity of the perovskite-like oxide La2-xSrxCuO4 (x=0.0, 0.5, 1.0) and the perovskite catalyst LaMnO3/ LaCuO3 was evaluated by complete oxidation of volatile hydrocarbons (HCs) in a mixture of toluene and methyl ethyl ketone (MEK) and carbon monoxide (CO) in a microflow analysis system combined with gas chromatography. The results showed that the light-off temperature (the 50% conversion temperature of the catalysts) of the Pt, Au/perovskite catalyst samples decreased significantly. The light-off temperature of the Au/LaSrCuO4 Au nanoparticle catalysts in the complete CO oxidation reaction reached a temperature of 150°C, lower than the Pt/LaSrCuO4 catalyst (170°C), allowing replacement of previous Pt catalysts with Au nanoparticle catalysts. The LaSrCuO4 catalyst had better oxidising activities than the La2CuO4 catalyst, indicating that the addition of strontium (Sr) has increased the catalyst activity, and demonstrates the potential for application in catalytic converters in motorcycles.

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Ionic liquids have recently been used as means of modulating the charge carrier properties of cuprates. The mechanism behind it, however, is still a matter of debate. In this paper we report experiments on ionic liquid gated ultrathin La2-xSrxCuO4 films. Our results show that the electrostatic part of gating has limited influence in the conductance of the cuprate in the gate voltage range of 0 to -2 V. A non-electrostatic mechanism takes over for gate voltages below -2 V. This mechanism most likely changes the oxygen concentration of the film. The results presented are in line with previous X-ray based studies on ionic liquid gating induced oxygenation of the cuprate materials YBa2Cu3O7-x and La2-xSrxCuO4 [ABSTRACT FROM AUTHOR]

Ionic liquids have recently been used as means of modulating the charge carrier properties of cuprates. The mechanism behind it, however, is still a matter of debate. In this paper we report experiments on ionic liquid gated ultrathin La2-xSrxCuO4 films. Our results show that the electrostatic part of gating has limited influence in the conductance of the cuprate in the gate voltage range of 0 to -2 V. A non-electrostatic mechanism takes over for gate voltages below -2 V. This mechanism most likely changes the oxygen concentration of the film. The results presented are in line with previous X-ray based studies on ionic liquid gating induced oxygenation of the cuprate materials YBa2Cu3O7-x and La2-xSrxCuO4 [ABSTRACT FROM AUTHOR]

In order to gain deep insight into the origin of the large thermoelectric power and metallic electrical conduction observed for La2− xSr xCuO4 possessing a two-dimensional layered structure and the consequently obtained two-dimensional electronic structure, we investigate the energy–momentum dispersion and the lifetime of quasiparticles by using high-resolution angle-resolved photoemission spectroscopy. By calculating the thermoelectric power using the Bloch–Boltzmann theory and the experimentally obtained information about the electronic structure and electron scatterings, we found that the large thermoelectric power of La2− xSr xCuO4 is mainly brought about by the anisotropic electron scattering caused by the strong electron correlation, and that the two-dimensional electronic structure makes almost no important contribution to the large S( T) except for rather minor effect of the van Hove singularity near the Fermi level. [ABSTRACT FROM AUTHOR]

Abstract: A series of single crystal samples have for the first time been grown by the travelling-solvent floating-zone method. Instead of preheating the feed rod materials at intermediate temperatures, we directly preheat the starting materials at 1150°C. After that we grow Mn doped samples at 0.33mm/h, which is much slower than the widely adopted 1mm/h rate used in the single crystal growth of samples. We believe that these improvements are crucial for obtaining Mn substitution into without inducing impurity phases. The results of magnetic susceptibility measurements indicate that the onset superconducting transition temperature of Mn doped samples does not decrease rapidly, indicating that Mn doping is quite peculiar compared to other elemental doping cases. [Copyright &y& Elsevier]

The zero-field splitting D of the 8S7/2 ground singlet for the tetragonal Gd3+ center in La2-xSrxCuO4 is theoretically studied from the superposition model. Meanwhile, the g factor is also quantitatively investigated from the approximation formula including admixture of the ground 8S7/2 and the excited 6L7/2 (L=P, D, F, G) states via the spin-orbit coupling interactions. The calculated zero-field splitting and g factor are in reasonable agreement with the experimental data. It is found that the significant zero-field splitting can be ascribed to the average impurity-ligand bonding angles [≈ (θ1 + θ2)/2 ≈ 62°] related to the four-fold axis larger than that (≈ 54.74°) of the cubic case. Nevertheless, the experimental g factor close to 2 may be largely due to the very slight admixture of the ground 8S7/2 and the excited 6L7/2 states via the spin-orbit coupling interactions. [ABSTRACT FROM AUTHOR]

The zero-field splitting D of the 8S7/2 ground singlet for the tetragonal Gd3+ center in La2-xSrxCuO4 is theoretically studied from the superposition model. Meanwhile, the g factor is also quantitatively investigated from the approximation formula including admixture of the ground 8S7/2 and the excited 6L7/2 (L=P, D, F, G) states via the spin-orbit coupling interactions. The calculated zero-field splitting and g factor are in reasonable agreement with the experimental data. It is found that the significant zero-field splitting can be ascribed to the average impurity-ligand bonding angles [≈ (θ1 + θ2)/2 ≈ 62°] related to the four-fold axis larger than that (≈ 54.74°) of the cubic case. Nevertheless, the experimental g factor close to 2 may be largely due to the very slight admixture of the ground 8S7/2 and the excited 6L7/2 states via the spin-orbit coupling interactions. [ABSTRACT FROM AUTHOR]

Our recent experimental works on the field-induced and impurity-induced magnetic order in La2-xSrxCuO4 are reviewed. The muon-spin-relaxation (μSR) measurements of La2-xSrxCu1-yMyO4 (M=Zn, Ni) have revealed that both Zn and Ni impurities develop the magnetic order around x=0.115, though the effect of Zn on the development of the magnetic order is more marked than that of Ni. The field-induced magnetic order around x=0.115 pointed out from the neutron scattering experiments has also been investigated by the thermal conductivity measurements in magnetic fields. Marked suppression of the thermal conductivity by the application of magnetic fields parallel to the c-axis has been observed in x=0.10 and x=0.13, which appears to be in good correspondence to the development of the magnetic order. In conclusion, not only impurities but also vortex cores in the CuO2 plane seem to operate to pin the dynamical stripes of spins and holes, leading to the development of the magnetic order. [ABSTRACT FROM AUTHOR]

c-axis micro-bridges of La2-xSrxCuO4 (LSCO) single crystals were fabricated by the focused-ion-beam (FIB) etching method. Small rectangular LSCO pieces were fabricated by cutting and grinding single crystals of underdoped LSCO of x=0.09. The size of LSCO single crystals between electrodes was cut to 20×40μm2 in ab-plane by using the FIB etching method. Superconductor-insulator-superconductor (SIS) like-branch structures on I-V curves of the LSCO stacks were observed for the first time. The branch structures exhibited voltage jumps of several tens mV in the range of from 1.7 K to 5 K with temperature dependence. When the temperature is changed from 5 K to 1.7 K, the critical current and the next branch split into a few of small voltage jumps with the intervals of several mV in the range of from 0.1 mV and 2.0 mV. [ABSTRACT FROM AUTHOR]

We revisited the Cu nuclear spin–lattice relaxation of 63Cu-enriched high-Tc superconductors La2-xSrxCuO4 with x=0.13 (an underdoped sample) and 0.18 (an overdoped sample). From application of the impurity-induced NMR relaxation theory, we observed a remnant of the pseudo-spin-gap effect on the host Cu nuclear spin–lattice relaxation rate 63(1/T1T)host and the inhomogeneous slow fluctuation effect via the impurity-induced relaxation rate 63(1/τ1). The magnetic phase diagram with the pseudo-spin-gap temperatures Ts is presented. [Copyright &y& Elsevier]

Low temperature scanning tunneling microscopy and spectroscopy measurements have been performed on the optimally doped La1.85Sr0.15CuO4 (LSCO) single crystal at 4.2 K in a magnetic field of 6 T applied along the c axis. The spatial distribution of the local density of sates (LDOS) has been successfully obtained on the ab plane. Although the weak distribution of the zero-bias conductance has been observed, the significant change in LDOS originating from the vortex core states has not been observed within our resolution. This result suggests that the vortex core state is rather small in LSCO. [Copyright &y& Elsevier]

Ab initio molecular orbital (MO) calculations on model clusters of cuprate superconductor, La2-xSrx CuO4 (LSCO) for x=0.05–0.33, are performed to find the effective force for electron pairing. The model clusters are such as La8Cu4O16, La14Sr2Cu8O32 and several others. The superconducting transition is explained by the transition from the metallic states composed of the restricted Hatree-Fock (RHF) type orbital to the metallic states comprised of the unrestricted Hatree-Fock (UHF) type orbital at transition temperatures where the free energies of these states coincide. Below Tc the states comprised of the UHF type orbital are stable. The pairing for three axis directions seems important for appearance of superconductivity and this is realized at x=0.06. The stabilization energies for the UHF type state compared to the RHF type states are correlated well with the transition temperatures (Tc). The force for the stabilization is apparent through the configuration interaction of HOMOs and LUMOs where the binding by the La/Sr orbital is important. It implies that the mixing and the interaction of electrons in the CuO2 plane and those in the La/Sr layers is important for the formation of the electron pair in cuprate superconductor. [Copyright &y& Elsevier]

We report the frequency-dependent microwave conductivity, σ(ω)=σ1(ω)-iσ2(ω), of La2-xSrxCuO4 (LSCO) thin films in the frequency range between 45 MHz and 12 GHz. For LSCO films with x=0.04–0.07, which cross the phase boundary separating the insulating phase (x<0.06) from the superconducting phase (x>0.06), we observed a typical behavior of the Drude metal in the Hagen–Rubens limit above about 100 K. This suggests that the low-energy charge dynamics near the phase boundary is similar to that of the Drude metal, even if the doped holes self-organize into one-dimensional charge stripes. Moreover, for superconducting film with x=0.07, we observed a definite frequency-dependent feature in σ(ω) near Tc, suggesting that the contribution of the superconducting fluctuation to σ(ω) shows up. [Copyright &y& Elsevier]

The electronic states of La 2- x Sr x CuO 4 with 0.00 ≤ x ≤ 0.20 are studied by means of X-ray absorption spectroscopy (XANES, EXAFS) near the K -edge of Cu 2+ ion and the L- edges of La 3+ ion. It is found that characteristic white lines occurring near L II and L III edges of La 3+ ion show a slight energy shift depending on substituted Sr 2+ ions, x and temperature. The white lines suggest that unoccupied high-density 5 d π and 5 d δ bands of La 3+ ion just above a Fermi level transform to a hybridized single band of 5 d πδ at 78 K in the superconductors with x = 0.10, 0.16 and 0.20. On the other hand, the XANES spectra near the Cu- K edge including a pre-edge region do not depend on x and temperature in the region of 0.00 ≤ x ≤ 0.20. It is considered that there is no reconstruction of electronic states at the Fermi level in a Mott-Hubbard band gap between an O 2 p valence band and a Cu 3 d conduction band. The electronic states at the Fermi level are probably consisted of the unoccupied 5 d πδ band and an empty charge-transfer 3 d 9 L band at low temperature, bands of which occur in a band gap between a filled O 2 p valence band and an unoccupied O 2 p conduction band. The insulator-superconductor-metal transitions in La 2- x Sr x CuO 4 are related to the 5 d πδ and 3 d 9 L bands and holes, which site at a top region of the O 2 p valence band near the Fermi level produced by a substitution of La 3+ with Sr 2+ ions. [ABSTRACT FROM AUTHOR]

Neutron scattering is proved to be a vital probe in unveiling the magnetic properties of high temperature superconductors (HTSC). Detailed information about the energy and momentum dependence of the magnetic dynamics of HTSC have been obtained directly by this technique. Over the past decade by improving the crystal growth methods, large and high quality single crystals of HTSC, which are essential for a neutron scattering experiment, have become available. The results of neutron scattering measurements on such crystals have considerably enhanced our understanding of the magnetism in HTSC both in the superconducting (SC) and normal states. In this review, the neutron scattering results on two main HTSC families, La2-xSrxCuO4 (LSCOx) and YBa2CuO3O6+x (YBCO6+x), are considered with an emphasis on the most prominent properties of these materials that are now widely accepted. These include the presence of strong antiferromagnetic (AF) fluctuations even in optimally doped region of the phase diagram, neutron resonance peak that scales with SC transition temperature, Tc, incommensurate magnetic fluctuations (stripes), and a pseudogap in the normal state of underdoped materials.

Abstract: We fabricated small intrinsic Josephson junctions of by focused ion beam etching. Current–voltage characteristics were investigated in the temperature range from 4K up to around . Multi-branch structure was clearly observed in the temperature range of 4–12K. [Copyright &y& Elsevier]

Neutron scattering experiments for La1.85Sr0.15Cu0.98Ni0.02O4 (Tc=28 K) demonstrated that well-defined incommensurate peaks appear in the superconducting state, giving an enhancement of χ″(qIC,ω) at ∼1 meV associated with a sharpening of peak width. Thus, the Ni impurities induce low-energy excitations and smear the sharp edge structure in χ″(qIC,ω) reported from the Ni-free system. On the other hand, no clear signature of magnetic ordering was observed in the elastic channel even at the lowest temperature. We conjecture that spin fluctuations around Ni impurities never quench but gradually slow down over a wide space, in contrast to Zn doping which locally destroys superconductivity in a drastic manner. [Copyright &y& Elsevier]