Bound excitons in Sr2CuO3

We investigated temperature dependent optical spectra of the one-dimensional chain compound Sr2CuO3. The charge transfer transition polarized along the chain direction shows a strongly asymmetric line shape as expected in one-dimensional extended Hubbard model. At low temperature, the charge transfer peak shows a large blueshift and reveals additional sharp peaks at the gap. Even though many spectroscopic studies suggest that this material cannot have a bound exciton based on the one-dimensional extended Hubbard model, we attribute the additional sharp peaks to excitons, which come to exist due to the long-range Coulomb interaction.     

Magneto-electrogyration in cubic Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2

The simultaneous application of electric and magnetic fields on single crystals of Sr-, Ba-and Pb-dinitrate yields an additional term to the pure electrogyration and Faraday effect. The symmetric part of the fourth-rank tensor of this magneto-electrogyration has been completely determined with the aid of a high-resolution computer-aided polarimetric device. In Pb(NO₃)₂ a maximum magneto-electrogyration of about 10% of the magnitude of electrogyration is observed when a magnetic field of 1000 kA/m (1.2 Tesla) is applied along [111]. The effects in Sr(NO₃)₂ and Ba(NO₃)₂ are much smaller. Index of refraction, electrogyration, Faraday effect, and the new magneto-electrogyration obey the same sequence: Pb(NO₃)₂ > Ba(NO₃)₂ > Sr(NO₃)₂.     

Comparative photoemission study of Bi2(Sr,Ca)3Cu2O8+y and Bi1.7Pb0.3Sr2Ca2Cu3O10+y

The electronic structure of Bi-based 2223 single phase superconductor has been studied by ultraviolet and X-ray photoemission. By comparison with that of 2212 phase superconductor, we find a higher density of states nearE _F for 2223 phase. From analysis of the Cu 2p core-level spectroscopy, we obtain a relatively smaller charge transfer energy between copper and oxygen as well as the Coulomb repulsion energy on Cu site for 2223 phase. We relate these changes to the increase of hole concentration from 2212 to 2223 phase. The experimental results support the viewpoint that the transition temperature should be correlated with the density of states atE _F .     

Sr3SiO5:Eu2+和Sr3SiO5:Eu2+, Dy3+荧光粉的黄色长余辉性质

用高温固相法制备了Sr3SiO5:Eu2 和Sr3SiO5:Eu2 , Dy3 荧光粉.在紫外光辐照后, Sr3SiO5:Eu2 和Sr3SiO5:Eu2 , Dy3 荧光粉具有明亮的黄色长余辉,源于Eu2 的4f65d - 4f7的跃迁.紫外光激发停止后,Sr3SiO5:Eu2 的余辉时间是4 h以上.余辉衰减曲线和热释光曲线说明了引入Dy3 离子可以产生大量的深陷阱和浅陷阱.产生的深陷阱使余辉时间延长到6 h以上.由热释发光曲线,根据热释光的通用级公式拟合了陷阱深度.Sr3SiO5:Eu2 和Sr3SiO5:Eu2 , Dy3 荧光粉是有应用前景的黄色长余辉材料.     

Critical spin dynamics of the 2D quantum Heisenberg antiferromagnets Sr2CuO2Cl2 and Sr2Cu3O4Cl2

We report a neutron scattering study of the long-wavelength dynamic spin correlations in the model two-dimensional S = 1/2 square lattice Heisenberg antiferromagnets Sr2CuO2Cl2 and Sr2Cu3O4Cl2. The characteristic energy scale, omega(0)(T/J), is determined by measuring the quasielastic peak width in the paramagnetic phase over a wide range of temperature ( 0.2 less similarT/J less similar0.7). The obtained values for omega(0)(T/J) agree quantitatively between the two compounds and also with values deduced from quantum Monte Carlo simulations. The combined data show scaling behavior, omega approximately xi(-z), over the entire temperature range with z = 1.0(1), in agreement with dynamic scaling theory.     

Peltier-effect in the mixed state of (Bi,Pb)2Sr2Ca2Cu3Oδ

We present measurements of the Peltier-effect in the mixed state of Bi_1.76Pb_0.24Sr₂Ca₂Cu₃O_δ. The Peltier-coefficient broadens in a magnetic field quite similar to the resistivity and the thermopower. Comparison with the thermopower shows that Onsagers relation holds well. The occurrence of the Peltier-heat in the mixed state well below T_c implies that the electric current is accompanied by a large heat current. We show that the vortex contribution to the Peltier-heat is negligibly small. Therefore the heat current has to be attributed to normal quasiparticle excitations. Our results indicate that this quasiparticle contribution to the heat current remains large even at temperatures far below T_c.     

Sr3TaGa3Si2O14(STGS)单晶的晶格振动

根据空间群理论,预测了Sr3TaGa3Si2O14(STGS)单晶的振动模式,并分别计算了非极性和极性振动模式的Raman散射强度。测量了STGS晶体的Raman光谱,并对其振动模式进行了指认。实验结果表明STGS晶体具有6个A1对称类特征振动模式:波数为126cm-1的振动峰可指认为SiO4团簇、Sr原子和TaO6团簇间的相对平动;245cm-1的振动峰是SiO4团簇的扭曲振动和Sr—TaO6—Sr伸缩振动耦合的结果;特征峰557和604cm-1分别来源于O—Ta—O和O—Ga—O的伸缩振动;896cm-1谱带对应着两个SiO4四面体的O—Si—O伸缩振动;991cm-1的谱带对应着两个SiO4四面体的Si—O伸缩振动。实验结果和理论计算结果均确证了STGS晶体的层状结构,其弱的各项异性和压电模量归因于十面体结构单元的微弱形变。     

Self-assembled antidots in La2/3Sr1/3MnO3 thin films

In this work, we report on the controlled fabrication of a self-assembled network of antidots in highly epitaxial La_2/3Sr_1/3MnO₃ thin films grown on top of SrTiO₃ (1 0 0) oriented substrates. To promote self-assembly process, it is fundamental to select a unique surface atomic termination of the STO substrates and the appropriate growth conditions. The evolution of the structural and magnetic properties as a function of deposition parameters is analyzed to clarify the growth mechanism leading to the formation of this self-assembled network of antidots. This morphology is of high interest envisaging a new route for the design and fabrication of oxide-based magnetoelectronic devices.     

Anisotropic fluctuation magnetoconductivity in Bi2Sr2Ca2Cu3Ox thin films

Measurements of the fluctuation magnetoconductivity as a function of both the magnetic field up to 13 T and the temperature in thin films of Bi₂Sr₂Ca₂Cu₃O_x are presented. The variation of the magnetoconductivity with the magnetic field strength is quadratic at temperatures distantly above the critical temperatureT _c and changes to an entirely negative curvature nearT _c . The latter behavior is attributed to an inhomogeneous critical temperature in the films. The results are analyzed in terms of recent theoretical models for fluctuation-enhanced magnetoconductivity in layered superconductors. The magnetoconductivity in a magnetic field oriented normal to the copper-oxide layers is dominated by the orbital contribution of the Aslamazov-Larkin effect. The magnetoconductivity in the parallel orientation is distinctly smaller and provides evidence for the corresponding Zeeman contribution. The latter measurement also indicates that the Maki-Thompson process may be insignificant in Bi₂Sr₂Ca₂Cu₃O_x.     

Structural properties and charge ordered states in RMnO3 (R=La, Pr, Nd, Ca, Sr) and (La, Sr)2NiO4

Structural distortions arising from the condensations of two essential kinds of phonon modes: the triply degenerate rotational modes (phix, phiy, phiz) of MnO(6) and the doubly degenerate Jahn-Teller active modes (Q1, Q2) have been systematically investigated in the perovskite manganites. Microstructural features associated with certain types of distortions have been observed by transmission electron microscopy (TEM). In RMnO(3) and La(Sr)(2)NiO(4), we characterize the local structure, charge ordered states and orbital ordering by means of low-temperature TEM. We present direct evidence that the stripe modulation in La(Sr)(2)NiO(4) is indeed one-dimensional within each NiO(2) plane. Several typical kinds of defect structures, including antiphase boundaries and the 90 degrees -twin domains, appear commonly in the charge-ordered states.