Suppression of near-Fermi level electronic states at the interface in a LaNiO3/SrTiO3 superlattice

Standing-wave-excited photoemission is used to study a SrTiO3/LaNiO3 superlattice. Rocking curves of core-level and valence band spectra are used to derive layer-resolved spectral functions, revealing a suppression of electronic states near the Fermi level in the multilayer as compared to bulk LaNiO3. Further analysis shows that the suppression of these states is not homogeneously distributed over the LaNiO3 layers but is more pronounced near the interfaces. Possible origins of this effect and its relationship to a previously observed metal-insulator-transition in ultrathin LaNiO3 films are discussed.     

Oscillatory exchange coupling and positive magnetoresistance in epitaxial oxide heterostructures

Oscillation in the exchange coupling between ferromagnetic La(2/3)Ba(1/3)MnO3 layers with paramagnetic LaNiO3 spacer layer thickness has been observed in epitaxial heterostructures of the two oxides. This behavior is explained within the RKKY model employing an ab initio calculated band structure of LaNiO3, taking into account strong electron scattering in the spacer. Antiferromagnetically coupled superlattices exhibit a positive current-in-plane magnetoresistance.     

不同生长条件下BiFeO_3薄膜的显微拉曼光谱研究

使用显微拉曼散射技术观察了用脉冲激光沉积方法(PLD)在不同的生长条件下制备的BiFeO3薄膜的拉曼光谱,并且研究了薄膜的结构以及不同的生长条件对薄膜的结构和微结构的影响。与BiFeO3粉末的拉曼光谱比较,我们发现在N2气氛中,在LaNiO3缓冲层上沉积的BiFeO3薄膜具有单一的三方相和最完整的晶格结构。     

LaNiO3-δ 薄膜中的氧缺位及其对金属输运行为的影响

钙钛矿结构 LaNiO3 因其高电导的金属性输运行为, 有望作为电极材料在今后的氧化物器件工艺中发挥重要作用. 为了细致认识氧缺位对其金属输运的影响, 本文采用溶胶凝胶法在氧气、 空气和真空等气氛下烧结获得具有不同缺氧量的 LaNiO3 -δ 薄膜, 并利用 Mn3 + 的还原性进一步调整其缺氧量δ . 对这些样品的电阻率温度关系测量结果表明, 缺氧量δ > 0. 1 后薄膜的高温电阻率开始超过 Mott-Ioffe-Regel 极限, 变成“坏金属”; 增大δ 至0.2, 薄膜的低温剩余电阻率大幅度上升, 说明氧空位分布无序性导致的载流子局域化有明显作用. 以上样品的金属输运都呈非费米液体行为. 继续增加氧缺位浓度, 样品电阻率在低温a30 K 以下呈绝缘体温度关系, 同时高温金属态转变为费米液体行为, 说明钙钛矿结构镍酸盐的金属-绝缘体转变与费米液体输运之间或存在关联性.     

The surface hydro-oxidation of LaNiO(3-delta) thin films

The chemical structure and possible hydro-oxidation of LaNiO(3-delta) films were studied by means of tuneable high-energy X-ray photoelectron spectroscopy using synchrotron radiation. It was shown that the hydroxyl-containing phase, located near the film surface, may be attributed to the lanthanum and nickel hydroxide species. The thickness of a hydroxide-enriched layer was estimated from the oxide/hydroxide ratio measured at normal and grazing conditions. The hydroxide layer thickness was about 2 nm for step and/or exponential hydroxide spatial distribution.     

Asymmetric orbital-lattice interactions in ultrathin correlated oxide films

Using resonant x-ray spectroscopies combined with density functional calculations, we find an asymmetric biaxial strain-induced d-orbital response in ultrathin films of the correlated metal LaNiO3 which are not accessible in the bulk. The sign of the misfit strain governs the stability of an octahedral "breathing" distortion, which, in turn, produces an emergent charge-ordered ground state with an altered ligand-hole density and bond covalency. Control of this new mechanism opens a pathway to rational orbital engineering, providing a platform for artificially designed Mott materials.     

Dynamical mean-field theory of nickelate superlattices

Dynamical mean-field methods are used to calculate the phase diagram, many-body density of states, relative orbital occupancy, and Fermi-surface shape for a realistic model of LaNiO(3)-based superlattices. The model is derived from density-functional band calculations and includes oxygen orbitals. The combination of the on-site Hunds interaction and charge transfer between the transition metal and the oxygen orbitals is found to reduce the orbital polarization far below the levels predicted either by band-structure calculations or by many-body analyses of Hubbard-type models which do not explicitly include the oxygen orbitals. The findings indicate that heterostructuring is unlikely to produce one band-model physics and demonstrate the fundamental inadequacy of modeling the physics of late transition-metal oxides with Hubbard-like models.     

Bipolar resistive switching in BiFe_(0.95)Zn_(0.05)O_3 films

Bipolar resistive switching is studied in BiFe0.95Zn0.05O3 films prepared by pulsed laser deposition on （001） SrTiO3 substrate, with LaNiO3 as the bottom electrode, and Pt as the top electrode. Multiple steps of resistance change are ob- served in the resistive switching process with a slow voltage sweep, indicating the formation/rupture of multiple conductive filaments. A resistive ratio of the high resistance state （HRS） to the low resistance state （LRS） of over three orders of mag- nitude is observed. Furthermore, the conduction mechanism is confirmed to be space-charge-limited conduction with the Schottky emission at the interface with the top Pt electrodes in the HRS, and Ohmic in the LRS. Impedance spectroscopy demonstrates a conductive ferroelectric/interfacial dielectric 2-layer structure, and the formation/rupture of the conductive filaments mainly occurs at the interfacial dielectric layer close to the top Pt electrodes.     

Optical and magnetic characterisation of Co3+ and Ni3+ in LaAlO3: interplay between the spin state and Jahn-Teller effect

The coordination, the electronic structures and the spin of the ground state of Ni(3+) (3d(7)) and Co(3+) (3d(6)) introduced as impurities in LaAlO(3) are investigated through optical spectroscopy and magnetic measurements. The unusual trivalent valence state in both transition-metal ions was stabilised via a sol-gel process followed by high oxygen pressure treatments. We show that the crystal-field strength at the nearly O(h) transition-metal site in LaAlO(3) locates Ni(3+) and Co(3+) near the spin state crossover, yielding a low-spin ground state in both cases. We analyse how the interplay between the Jahn-Teller (JT) effect and the spin state affects the magnetic moment of the ion and its temperature dependence. The optical spectra reveal a JT effect associated with a low-spin ground state in Ni(3+) and with a thermally populated high-spin low-lying first excited state in Co(3+). The corresponding JT distortions are derived from structural correlations. We conclude that the JT effect is unable to stabilise the intermediate spin state in Co(3+). A low-spin ground state in thermal equilibrium with a high-spin low-lying first excited state is detected in diluted Co(3+)-doped LaAlO(3). These results are compared with those obtained in the parent pure compounds LaNiO(3) and LaCoO(3).     

Superconducting effects in Hg3-δAsF6

Superconducting properties of Hg_3-δAsF₆ have been investigated by a.c. magnetic susceptibility measurements in the temperature range 1.25–4.2 K and magnetic field range 0–0.05 T and by resistivity measurements in the temperature range 1.25–4.2 K. The properties are attributed to mercury dispersed in isolated regions throughout the sample.     

Analysis of the ν3 band of 12CH3D at 7.6 μm

The previously reported (J. Mol. Spectrosc.68, 195–222 (1977)) study of the CH₃D spectrum occurring at 1033–1270 cm^?1 which was mainly concerned with the ν₆ fundamental has now been extended to cover the region 1270–1420 cm^?1. In all, 342 transitions belonging to the ν₃ band are now assigned. Both the ν₃ and ν₆ bands are processed simultaneously taking into account of the Coriolis interaction between them, and the fitting of all the experimental data led to 21 significant spectroscopic constants for the states v₆= 1 and v₃ = 1 of CH₃D.     

Relativistic calculations of 3s2 1S0-3s3p 1P1 and 3s2 1S0-3s3p 3P1,2 transition probabilities in the Mg isoelectronic sequence

Using the multi-configuration Dirac-Fock self-consistent field method and the relativistic configuration-interaction method,calculations of transition energies,oscillator strengths and rates are performed for the 3s 2 1 S 0-3s3p 1 P 1 spinallowed transition,3s 2 1 S 0-3s3p 3 P 1,2 intercombination and magnetic quadrupole transition in the Mg isoelectronic sequence(Mg I,Al II,Si III,P IV and S V).Electron correlations are treated adequately,including intravalence electron correlations.The influence of the Breit interaction on oscillator strengths and transition energies are investigated.Quantum electrodynamics corrections are added as corrections.The calculation results are found to be in good agreement with the experimental data and other theoretical calculations.     

Magnetic and transport properties of Dy substituted layered perovskite La1.3Sr1.7Mn2O7

The effect of Dy substitution for La site in layered manganese oxides La1.3-x Dyx Sr1.7 Mn2O7 on the magnetic and electrical properties has been investigated.With the La 3+ substituting by Dy3+,the long range three-dimensional ferromagnetism transition and the insulator-metal transition disappear.These effects are attributed to the lattice distortion due to the substitution of the smaller Dy3+.Addtionally,the small Dy3+ is inclined to occupy the R site which is in the rock-salt layer,then the distribution of La,Sr,Dy ions in Dy-doped sample should be more orderly than that in La1.3 Sr1.7 Mn2O7,so there is only one insulator-metal transition in the ρ-T curve of the sample with x = 0.05 and x = 0.1.     

Far ultraviolet reflectance spectra of CeF3, PrF3 and NdF3

Near-normal incidence reflectance measurements are carried out on thin films of CeF₃, PrF₃ and NdF₃ in the energy range of 6–40 eV. Tentative interpretations are given for different observed structures.     

Observation of interface plasmon excitation in photoemission spectroscopy from the heterostructures Cu/RbF/GaAs(100) and Cu/RbF/Ge(100)

Synchrotron radiation photoelectron spectra taken at 100 eV photon energy have been measured to characterize the interface reactions of the metal-insulator-semiconductor systems Cu/RbF/GaAs(100) and Cu/RbF/Ge(100). In comparision, similar sequences are studied on the Cu/GaAs(100) and Cu/Ge(100) interfaces without the RbF interlayer. After Cu-deposition of 1–4 Å on RbF-covered (10–14 Å) GaAs and Ge surfaces, shoulder peaks appear on both the Ga 3d and Ge 3d core levels. The shoulder peaks are shifted 1.1 and 1.4 eV to higher binding energy for the Ga 3d and Ge 3d levels, respectively. The Rb 4p and F 2p peak positions are slightly shifted between 0.25 and 0.5 eV. The broad second Ga 3d and Ge 3d peaks can be correlated to plasmon loss of electrons from these levels in a two-dimensional Rb metal-like layer formed at the Cu/RbF interface. The excitation energy of a Rb surface plasmon in a Cu-Rb-RbF system is calculated to be 1.3 eV.     

Galvanomagnetic effects in Fe40Ni40B20

Hall effect and magnetoresistance measurements on the amorphous ferromagnet Fe₄₀Ni₄₀B₂₀ are reported. Both properties are approximately independent of temperature (1.5–300 K) and related to magnetization. The extraordinary Hall coefficient is 3.5 × 10^?8 m³/As. The temperature dependence of the resistivity (1.5–30 K) is also reported.     

Inversion of conductivity type in Bi2Te3−xSx crystals

Transport parameters and optical properties of Bi₂Te_3?xS_x single-crystals with x=0–0.18 were studied. With increasing sulphur content the concentration of free current carriers decreases up to x=0.12, due to the interaction of S^x_Te defects with antisite defects Bi^′_Te, and then the p-type conductivity changes to the n-type. The optical gap of Bi₂Te_3?xS_x crystals increases with increasing S content. The obtained results led to the preparation of Bi₂Te₃-Bi₂Te_3?xS_xp–n junction by the heat treatment of p-type Bi₂Te₃ in S vapours.     

Search for finite-mass neutrinos in the decay π+→μ+vμ

If neutrinos possess non-zero mass, pion decay might have small decay branches to neutrino states with large masses. We have searched for such branches in the decay of pions produced at the Indiana University Cyclotron. The energy spectrum of decay muons shows no evidence for such neutrino branches and if these decays do exist, their branching ratios must be less than 10^?2 to 10^?3 for neutrino masses in the ranFge 7–33 MeV.     

On the Auger-photoelectron coincidence spectroscopy spectra of Cu(100), Cu metal and CuOx/Cu surface

The M₃–VV Auger-photoelectron coincidence spectroscopy (APECS) spectrum of Cu(100) and the L₃–VV APECS spectra of Cu metal and CuOx/Cu surface are analyzed in detail. The narrowing and energy shift of the photoelectron line in the M₃–VV APECS spectrum is well predicted by the present theory. The spectrum shows the presence of the M₂–M₃(V)–VV(V) decay in which a hole in the 4s band hops away prior to the decay of M₃ hole. The analysis of the L₃ photoelectron spectra of Cu metal measured in coincidence with the ³F or ¹G Auger line raises a question concerning the presence of two different core–hole states upon the L₃ level ionization recently proposed by Thurgate and Jiang [Surf. Sci. 466 (2000) L807]. The analysis of the L₃–VV APECS spectrum of CuOx/Cu shows that the final-state charge–transfer interaction plays an important role in CuO.     

Temperature and induced electric field dependence on the phase transition of 9/70/30, 9/65/35 and 9/60/40 PLZT ceramics

In this work, Pb_0.91La_0.09(Zr_1–xTi_x)_0.9775O₃ ceramics where x = 0.3, 0.35 and 0.4 (the composition near MPB) were prepared by solid solution method. After fabrication process, electrical property was measured by LCR meter. Polarization and induced strain behavior of the samples were investigated by using interferometry technique modified with Sawyer–Tower circuit at various temperatures. The results of dielectric, polarization and induced strain properties were due to the Zr/Ti ratios, which changed their behavior when temperature was varied (30–70 °C). The normal to macro-micro domains to relaxor and paraelectric phase transition was demonstrated which is related to linear or nonlinear increase of polarization and induced strain as a function of applied subswitching electric field.