Characteristic fields of a Bi2Sr2CaCu2Oy crystal

The field dependences of the transverse resistance of a Bi₂Sr₂CaCu₂O_y (BSCCO) layered superconducting single crystal with T _c0≥92 K are studied in a perpendicular (H⊥(ab)) pulsed magnetic field up to 50 T in a wide temperature range, 4.2–300 K. The temperature dependences of the characteristic fields identified with the “irreversibility curve” and the field corresponding to the nucleation of the superconducting phase are determined. The results obtained for the latter field are compared with the theoretical dependences.     

Bi2Sr2-xLaxCaCu2Oy体系电子结构的光电子能谱研究

Bi系铜氧化物超导体具有双Bi-O层结构,带结构理论计算显示,除Cu-O面参与金属导电外,Bi-O层的Bi6p-O2p带也穿过了费米能,对费米面有贡献.因此,有必要对Bi-O层的作用进行实验研究.本文用X-射线光电子能谱研究了Bi2Sr2-xLaxCaCu2Oy体系中La原子的占位及Bi和Cu原子的价态变化.分析表明,La主要替代了Sr位(位于Bi-O层和Cu-O层之间)的Sr,随着La的搀杂,Bi的平均价态上升,Cu的平均价态下降.     

Synthesis and properties of HgI2 intercalation of Bi2Sr2CaCu2Oy superconductor

Polycrystalline or single crystals of HgI₂ intercalated Bi₂Sr₂CaCu₂O_y (Bi2212) have been synthesized and their properties have been studied together with those of HgBr₂ intercalates. Single crystals of HgI₂ intercalated Bi2212 were synthesized by a stepwise intercalation method using iodine intercalate as a secondary host material. These could not be obtained through direct intercalation methods by which polycrystalline sample were obtained. From ac susceptibility and resistivity measurements, superconducting onset temperature (T_con) for polycrystalline HgI₂ intercalate was found to be 82 K which was higher than that of the host (75 K). On the other hand, T_con for single crystal HgI₂ intercalate was shown to be 79–80 K which is lower than that of host (95–97 K). The effect of HgI₂ or HgBr₂ intercalation on T_c tried discussion from the view point of hole doping and interblock coupling effect.     

Characteristic features of the formation of the resistive state in a Bi2Sr2CaCu2Oy crystal

The effect of a magnetic field H⊥(ab) on the transverse current-voltage characteristics (IVCs) of the mixed state of a single crystal of the layered superconductor Bi₂Sr₂CaCu₂O_y (BSCCO) is investigated. It is established that in a wide range of temperatures and fields above the irreversibility line the initial part of the IVC is described by the law V∝I ^γ with γ≃1. As the current increases further, this law is replaced by a section where V∝exp(I). It is established that the multivalued, multibranch characteristics, interpreted as a manifestation of an internal Josephson effect, do not change appreciably when the crystal passes into a state with nonzero linear resistance. The character of the dependence of the characteristic switching current on the first resistive branch, I _J (H,T), is determined. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 543–548 (25 October 1999)     

Effects of growth rate and buffer-layer on Bi2Sr2CaCu2Oy thin film fabrication

The effect of the growth rate on the Bi₂Sr₂CaCu₂O_y (Bi2212) thin film quality on MgO substrate is investigated at several growth rates from 0.175 to 3 nm/min. The maximal step height on the film surface is improved from about 100 to 6 nm by the reduction of growth rate to 0.5 nm/min and simultaneously the superconducting critical temperature attaining to a zero resistance T_c(R=0), is also improved from 50 to 63 K. The surface morphologies of the upmost Bi-superconducting thin films with the intermediate layers on MgO substrate is also studied in contrast to that deposited directly on the MgO substrate.     

Noise spectral power and non-equilibrium dynamics of vortices in the mixed state of Bi2Sr2CaCu2Oy

A model is proposed to explain the observed noise spectral power generated by the moving vortex lattice in Bi₂Sr₂CaCu₂O_y single crystals. The analysis is based on the observations that the noise generated is due to the vortex velocity rather than the thermodynamic phase of the material. The motion of vortices induces a gradual transition of the vortex lattice from the plastic flow to the uniform flow with increasing magnetic field. The influence of the disorder on the dynamics of vortices is such that a uniform distribution in the activation barrier width will exist. This distribution will affect the attempt frequency of the flux line hopping and consequently the spectral shape of the noise generated. The model provides physical basis to the fact that the observed 1/f-noise power corresponds to the smaller velocity of the vortex lattice, while the deviation from the 1/f-spectrum corresponds to the larger velocity region. The results of the simulation are compared to recent experimental measurements where good agreement has been achieved.     

In situ electron-microscope investigation of phase formation and defects in Bi2Sr2CaCu2Oy single crystals on heating

A strong nonthermal influence of electron irradiation on the formation of new phases and structural defects has been found in an in situ study of structural transformations of Bi₂Sr₂CaCu₂O_y crystals under heating. The stability of the modulated structure and stacking faults with respect to heating by an electron beam and in the absence of irradiation was investigated. Fiz. Tverd. Tela (St. Petersburg) 39, 457–462 (February 1997)