Superconducting Glass State Research Articles

Memory effects in YBa2Cu3O7−δ single crystal

Measurements of the time dependence of zero-field-cooled (ZFC) and field-cooled (FC) magnetization M in YBa 2 Cu 3 O 7-δ single crystal have been performed as a function of temperature and magnetic field. The appearance of an echo-like feature in the decay rate S = dM/d ln t at an observing time t equal to the waiting time t w during which the specimen was prepared at a given field H 0 and temperature T reveals aging effects in the superconducting state. Similar phenomena reported in spin glasses seem to validate the picture of a superconducting glass state in YBa 2 Cu 3 O 7-δ .

Glass behavior and power dissipation in htsc near the transition point

The superconducting glass state behavior in samples of Y 1 − x Ba 2Cu 30 7 − δ, YBa 2(1 − x) Cu 3O 7 − δ, YBa 2Cu 3(1 − x) O 7 − δ and BiSrCa CuO (2212 and 2212 + 2223 phases) has been investigated at 0.8 ⩽ t ⩽ 1.0. It was found that the shape of the J-U relationship correlates with the morphology and composition of the interface between the adjacent misoriented grains. Local overheating and thermal relaxation phenomena play an important role in determining the nature of the resistive state below T c . It is shown that the J c ( t) dependences vary from the (1 − t) 2 type, in the case of an amorphous phase at the grain boundary interface, to the (1 − t) 1 2 type, corresponding to the interface with an extra CuO layer.

Muon-spin rotation experiments in high-Tc superconductors and related materials

Recent muon-spin rotation µSR experiments in high-T c superconductors and related antiferromagnetic materials are reviewed. The possibilities and the limitations of the µSR method for investigating these materials are briefly discussed. In a high-T c superconductor, µSR is an ideal tool with which to study the local magnetic field distribution at the muon site, allowing a determination of the London penetration depth. It is further shown that µSR experiments may contribute to the microscopic understanding of the superconducting glass state in the high-T c oxides. In the related antiferromagnetic materials µSR is a sensitive method for detecting frozen local magnetic moments.

What is the origin of “glassy” behavior in the high-T c oxides?

The anomalous low-field magnetic properties of the high-T c oxide crystals have been interpreted alternatively in terms of a superconductive glass state or, more recently, giant flux creep. The glass picture as proposed assumes the occurrence of intra granular Josephson junctions on a length scale small compared to the penetration depth, and has been used to explain the properties of both single-crystal and ceramic samples. The flux creep picture deals only with pinning forces and ignores weak links, and thus far has been applied only to single crystals. We show here that neither of these models adequately describes the behavior of ceramic materials. A physically accurate picture of such materials must take into account inter granular Josephson junctions and resultant grain decoupling at low magnetic fields.

VERY ANOMALOUS HYSTERESIS IN GRANULAR HIGH TEMPERATURE SUPERCONDUCTING CERAMICS

The observation of a very anomalous hysteresis in the resistivity behavior of granular high temperature ceramic superconductors, under the influence of a low magnetic field, in the critical temperature region [TR, Tc] is discussed. After eliminating various a priori possible mechanisms, such as that of superconductive glass state, we present arguments strongly suggesting that the effect comes from flux pinning effects and the peculiar grain “boundary condition” effects.

FLUX TRAPPING AND SUPERCONDUCTIVE GLASS STATE IN La2CuO4−y: Ba

The mixed copper-oxide superconductors recently discovered are not classical superconductors but have been shown to exhibit some properties of a superconducting glass. The grains in these ceramics are not uniform bulk materials but rather a composition of coupled superconducting clusters. Evidence for the superconducting glass state was first seen in the susceptibility, chi, and magnetic-moment measurements of powder samples of La/sub 2/CuO/sub 4-y/:Ba from 1.9 to 35 K in magnetic fields up to 1.5 T. The diamagnetism observed in the zero-field-cooled state was considerably larger than when field cooled. Figure 1(b) shows typical sequences of temperature dependences expected of a glass state. After zero-field cooling the sample and switching on a 0.03-T field, chi is measured at point A. On heating sample, point B on curve 1 is reached. On recooling, a nearly temperature-independent susceptibility is measured. With further heating, point B is passed until point C is reached on curve 1, where on recooling, a temperature-dependent slope smaller than that of curve is followed. On further heating, curve 1 becomes reversible past point D. This same value D is reached by field cooling from 35 K. In field cooling past D, curve 2 is followed reversibly on a timemore » scale of two hours.« less

TRANSPORT PROPERTIES FOR IMPERFECT LnBa_2_Cu_3_O_7-y_ SINGLE CRYSTALS

摘要 在LnBa_2_Cu_3_O_7-y_单晶上的一系列实验事实表明: 体内存在的结构不完整性和组成不均匀性都对其正常态电阻率、常一超导转变行为、超导临界温度, 以及临界电流等产生重要影响. 作者认为: 与单相多晶LnBa_2_Cu_3_O_7-y_样品相似, 非理想的单晶体也存在着超导玻璃态效应。 Abstract A series of experimental facts for LnBa_2_Cu_3_O_7-y_ single crystals indicate that imperfect structure and non-uniformity composition in samples have an important effect on their normal state resistivity, normal-superconductive transition behavior, T。and critical current and so forth. We think that in imperfect single crystals, there also exist superconductive glass state effects, similar to single phase polycrystal LnBa_2_Cu_3_O_7-y_ samples. 作者及机构信息 方明虎；夏健生；孙敦明；；陈健；；陈祖耀；张其瑞 1. 中国科学技术大学物理系 Authors and contacts 参考文献 施引文献

Time dependent magnetic response in a GdBa 2Cu 3O 7−δ superconductor: Flux creep or superconducting glass state?

Time dependent magnetic response has been examined for a GdBa 2Cu 3O 7−δ superconductor. Logarithmic time dependence of the magnetic relaxation is observed over several decades in 1n(t). A temperature and field dependent prefactor A(T,H) = dM/d1n(t) is observed for these materials for relaxation from the zero field cooled (ZFC) state and from the remanent state. The Meissner state (field cooled (FC)) is characterized by zero relaxation. This magnetic relaxation is discussed in terms of a conventional flux creep model and in light of the superconducting glass state model. It is concluded that since the relaxation coefficient A disappears at the glass transition temperature, and not at T c, the superconducting glass state model is most descriptive of these results.

The behaviors of superconductive glass state in high-T c superconducting ceramics

The behaviors of superconductive glass state in single phase GdBa 2Cu 3O 7−y, YBa 2Cu 3O 7−y ceramics have been studied systematically by measuring the microstructure, superconductive parameters, I–V characteristics, etc.. The grain-boundary Josephson effect and percolation nature etc. have been observed and explained satisfactorily with 3-D network of Josephson junctions.

Magnetic susceptibility of rapidly solidified YBa2Cu3O7−x superconductors

The superconducting YBa2Cu3O7−x phase has been produced through a novel rapid solidification processing route yielding a high-quality granular superconducting phase. Features in the magnetic susceptibility as measured at various fields can be attributed to important transitions in the superconducting behavior of these materials. At low fields (∼20 Oe) anomalies in the susceptibility arise from decoupling of the grains in these polycrystalline materials. Susceptibility response at higher fields (∼100 Oe) is representative of randomly oriented superconducting grains which show local superconducting current densities comparable to those of single crystals. At even higher fields features consistent with Muller’s superconducting glass state model are observed.

Magnetism and microstructure of YBa2Cu3O7-x superconductors produced by rapid solidification.

The superconducting $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ phase has been produced through a novel rapid solidification processing route yielding a high-quality granular superconducting phase. A detailed study of the magnetic properties indicates important features relevant to current carrying capacity. Low-field magnetization data reveal that weakly coupled superconducting grains decouple at fields of approximately 20 Oe so that the magnetization measurements at higher fields are reflective of intragranular processes exclusively. The high-field data reveal significant irreversibility as well as nonergodic susceptibility behavior consistent with the recently proposed superconducting glass state.

Superconducting glassy state in high-Tc oxides

Abstract Starting with the first observation of a superconducting glassy state in La 2- x Ba x CuO 4 ceramics by susceptibility and magnetic moment measurements, recent microwave absorption experiments as well as magnetic relaxation effects will be presented and discussed in the light of very large scale Monte Carlo computer simulations. The origin of the superconducting glass state is inferred as being due to Josephson junctions or weak links partly internal to the ceramic grains or single crystals occuring at twin boundaries.

Low-field microwave absorption in the superconducting copper oxides.

A nonresonant microwave absorption has been observed at fields below the thermodynamic critical field, ${H}_{c1}^{(T)}$, in the new copper oxide superconductors. This is associated with flux slippage and allows an estimation of the average area of the uniform phase in the superconducting glass state.

The superconducting glass transition in YBa2Cu3O7 − δ

The electrical resistance and the d.c. magnetization of bulk sintered Y Ba 2 Cu 3 O 7− δ were measured for magnetic fields, H, in therange 1 Oe to 5 kOe near the superconducting transition temperature. The onset temperature for hysteresis, T(H), determined from the resistance measurements was found to obey the relation H α [ 1 − T(H) T(O) ] γ with γ = 1.49 ±.04. The results are evidence for the existence of the superconducting glass state in this material and provide quantitative agreement with the Almeida-Thouless prediction of γ = 1.5.

The Discovery of a Class of High-Temperature Superconductors

The exceptional interest in the new class of oxide superconductors and the importance of these materials are discussed together with the concepts that led to their discovery. The discovery itself and its early confirmation are summarized, including the work until the beginning of 1987. The observation of a superconductive glass state in percolative samples is also discussed.

Flux trapping and superconductive glass state in La2CuO4-y:Ba.

Susceptibility and magnetic-moment measurements from 1.9 to 35 K in magnetic fields up to 1.5 T in powder samples of La/sub 2/CuO/sub 4-//sub y/:Ba are reported. The diamagnetism observed in the zero-field--cooled state is considerably larger than under field cooling. The former is metastable like the magnetic moment induced after switching the field off. These observations indicate the existence of a superconductive glass state.

Metastability and Glass State in Superconducting La2CuO4-y: Ba

Susceptibility measurements for 1.9 to 35K in magnetic field from 0.015 to 1.5 Tesla in superconducting La2CuO4-y: Ba are reported. The diamagnetism created by the zero-field cooling and switching on a field shows non-exponential time-decays indicating an existence of superconducting glass state. Measuring with different fields, a quasi de Almeida-Thouless line separating ergodic from nonergodic areas in H–T plane has also been obtained.