Crystals Of High-temperature Superconductors Research Articles

Application of third-order nonlinear optical materials in complex crystalline chemical reactions of borates

Abstract In order to explore the application of third-order nonlinear optical (NLO) materials in complex borate crystalline chemical reactions, the laser light source with limited wavelength range can be extended to ultraviolet (UV) and deep UV region by using NLO crystal materials and frequency conversion technology, which has become a hot research direction of deep UV light source. The experimental results show that the UV cutoff edge of the grown KLi(HC3N3O3)·2H2O crystal is 237 nm. The refractive index of the crystal was measured by prism coupling technique, and the Sellmeier equation of the refractive index of the crystal was fitted. The chemical bond of the crystal is a fundamental means to understand the relationship between structure and properties. With the emergence of a large number of hybrid functional crystals, the composition and structure of crystals become more complex, and the chemical bond theory has also been greatly developed, and then the chemical bond theory of meta crystals or complex crystals has emerged. Once proposed, the theory has been widely used, such as analyzing the eligibility of luminescent crystals, NLO crystals and high-temperature superconductor crystals. NLO materials are the dominant field of China in the world. Crystals with good nonlinear behavior have more complex crystal structures, due to the theory of amorphous structure, the exploration of this aspect is particularly difficult. For the first time, the influence of the composition of rare earth-doped bismuth borate glass on the crystal precipitation and glass microstructure of NLO materials was systematically studied, which laid a theoretical foundation for further development and understanding of new bismuth borate optical systems.

Resistivity Studies by Multiterminal Transport Measurements on Single Crystal YBa2Cu3O7−δ

Multiterminal transport studies provide a powerful technique to investigate vortex structure and correlations in the vicinity of the vortex solid-to-liquid transition in single crystals of high temperature superconductors. Recent results are described, including new contact configurations, allowing both longitudinal and transverse vortex correlations to be studied in one crystal during a single temperature sweep at constant field.

Optical excitations with even symmetry in insulatingcuprates

An excitonic cluster model, which can take into account both the strongcorrelation effect of 3d electrons and the itinerant nature of electronicexcitations, and consequently both the bound and unbound states of electronsand holes on the same footing, is applied to describe optical excitations witheven symmetry in insulating cuprates, i.e. parent crystals ofhigh-temperature superconductors. These states are observable in large-shiftRaman scattering and two-photon absorption spectra.

Excitonic cluster model of strongly correlated electronic systems

An excitonic cluster model is proposed todescribe the optical responses of strongly correlated electronicsystems, e.g. antiferromagnetic insulators of parent crystals ofhigh-temperature superconductors. This model can take intoaccount both the strong correlation effect of 3d-electrons andthe itinerant nature of electronic excitations. Consequentlyboth the electron-hole bound and unbound states can be describedon the same footing. As a result, we can resolve the mystery ofresonance enhancement of 2-magnon Raman scattering, and removeinconsistencies in the understanding of the absorption spectrum,the photoconductivity spectrum, and large-shift Raman signals.

Use of solar furnaces under orbital-flight conditions

Use of direct solar heating under space conditions for the production of materials with prescribed properties has a number of advantages over resistance and optical heaters used earlier for these purposes. Using SP-1.0 and Zenit SP-01-5 furnaces designed for the Alpha international space station as examples, the author analyzed the technical capabilities of solar furnaces as compared to resistance and optical heaters under space conditions in the production and investigation of: disilicides of transition metals of high purity; compositions based on the Al-Pb system, which is an antifriction material; photostimulated epitaxial films; crystals of CdTe and Bi2Te3 from melts; tantalum disilicide; single crystals of high-temperature superconductors and other materials.

Collective-pinning theory and the observed vortex dynamics in RBa2Cu3O7- delta crystals.

We establish a framework for the analysis of magnetization data on high-temperature superconductor crystals that allows direct comparison with vortex-pinning theory. When the magnetization loops exhibit scaling behavior, as they do over a large part of the B-T plane for R${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ crystals, the effective pinning energy ${\mathit{U}}_{\mathrm{eff}}$ has to contain power-law field dependences for the characteristic energy and current scales ${\mathit{U}}_{0}$ and ${\mathit{J}}_{0}$; these power-law exponents can be obtained directly from the data. Many regimes of collective-pinning (CP) theory do predict such power laws, but none yield exponents in agreement with those that are measured. The discrepancy appears to arise because ${\mathit{U}}_{0}$ is observed to decrease with B, in contrast to the CP predictions. \textcopyright{} 1996 The American Physical Society.

Improper ferroelectric phase due to condensation of two order parameters in crystals of high-temperature superconductors

Abstract Using group-theoretical methods it is shown that improper ferroelectric phase may arise in high-temperature superconductors (HTSC) where high-symmetry phases have space groups D 4h 1 or D 4h 17. Their appearance is caused by condensation of order parameters (OP's) transforming two irreducible representations (IR's). The most typical phase diagrams are considered, as well as temperature dependence of OP's and the basic structural mechanism of the ferroelectricity arising in the HTSC.

Anisotropic current flow and demagnetization corrections in the Bean model

In the present paper corrections to the standard Bean model are considered which turn out to be essential for the analysis of magnetization measurements on single crystals of high temperature superconductors. Because of the sensitivity of the Bean model to the actual geometrical shape of the superconductor in the plane perpendicular to the field direction, appropriate equations have to be employed. This becomes even more important if anisotropic current flow, e.g. in the ac plane of YBCO single crystals, is considered. In addition, demagnetization corrections of the measured magnetization curves are introduced. An analysis of experimental results based on these extensions of the standard Bean model shows that demagnetization corrections affect the j c values in the crystal by +21% to −6% in the worst case, whereas the inclusion of anisotropic current flow leads to an enhancement of current anisotropies by at least 100%.