The Experts below are selected from a list of 180 Experts worldwide ranked by ideXlab platform
J. C. Phillips - One of the best experts on this subject based on the ideXlab platform.
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Hard-Wired Dopant Networks and the Prediction of High Transition Temperatures in Ceramic Superconductors
Journal of Superconductivity and Novel Magnetism, 2010Co-Authors: J. C. PhillipsAbstract:I review the multiple successes of the discrete hard-wired dopant network model ZZIP, and comment on the equally numerous failures of continuum models, in describing and predicting the properties of Ceramic Superconductors. The prediction of transition temperatures can be regarded in several ways, either as an exacting test of theory, or as a tool for identifying theoretical rules for defining new homology models. Popular “first principle” methods for predicting transition temperatures in conventional crystalline Superconductors have failed for cuprate HTSC, as have parameterized models based on CuO2 planes (with or without apical oxygen). Following a path suggested by Bayesian probability, we find that the glassy, self-organized dopant-network percolative model is so successful that it defines a new homology class appropriate to Ceramic Superconductors. The reasons for this success in an exponentially complex (Non-Polynomial Complete, NPC) problem are discussed, and a critical comparison is made with previous polynomial (PC) theories. The predictions are successful for the superfamily of all Ceramics, including new non-cuprates based on FeAs in place of CuO2.
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Hard-Wired Dopant Networks and the Prediction of High Transition Temperatures in Ceramic Superconductors
Advances in Condensed Matter Physics, 2010Co-Authors: J. C. PhillipsAbstract:I review the multiple successes of the discrete hard-wired dopant network model ZZIP, and comment on the equally numerous failures of continuum models, in describing and predicting the properties of Ceramic Superconductors. The prediction of transition temperatures can be regarded in several ways, either as an exacting test of theory, or as a tool for identifying theoretical rules for defining new homology models. Popular “first principle” methods for predicting transition temperatures in conventional crystalline Superconductors have failed for cuprate HTSC, as have parameterized models based on CuO2 planes (with or without apical oxygen). Following a path suggested by Bayesian probability, it was found that the glassy, self-organized dopant network percolative model is so successful that it defines a new homology class appropriate to Ceramic Superconductors. The reasons for this success in an exponentially complex (non-polynomial complete, NPC) problem are discussed, and a critical comparison is made with previous polynomial (PC) theories. The predictions are successful for the superfamily of all Ceramics, including new non-cuprates based on FeAs in place of CuO2.
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universal non landau self organized lattice disordering percolative dopant network sub tc phase transition in Ceramic Superconductors
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: J. C. PhillipsAbstract:Ceramic Superconductors (cuprates, pnictides, etc.) exhibit universal features in both Tcmax and in their planar lattice disordering measured by EXAFS, as reflected by three phase transitions. The two highest temperature transitions are known to be associated with formation of Jahn–Teller pseudogaps and superconductive gaps, with corresponding Landau order parameters, but no new gap is associated with the third transition below Tc, and its origin is mysterious. It is argued that the third subTc transition is a dopant glass transition, which is remarkably similar to topological transitions previously observed in chalcogenide and oxide alloy network glasses (like window glass).
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Prediction of High Transition Temperatures in Ceramic Superconductors
arXiv: Superconductivity, 2009Co-Authors: J. C. PhillipsAbstract:The prediction of transition temperatures can be regarded in several ways, either as an exacting test of theory, or as a tool for identifying theoretical rules for defining new homology models. Popular "first principle" methods for predicting transition temperatures in conventional crystalline Superconductors have failed for cuprate HTSC, as have parameterized models based on CuO2 planes (with or without apical oxygen). Following a path suggested by Bayesian probability, we find that the glassy, self-organized dopant network percolative model is so successful that it defines a new homology class appropriate to Ceramic Superconductors. The reasons for this success are discussed, and a critical comparison is made with previous theories. The predictions are successful for all Ceramics, including new non-cuprates based on FeAs in place of CuO2.
Hikaru Kawamura - One of the best experts on this subject based on the ideXlab platform.
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Aging effect in Ceramic Superconductors.
Physical review letters, 2001Co-Authors: Per Nordblad, Hikaru KawamuraAbstract:A three-dimensional lattice of the Josephson junctions with a finite self-conductance is employed to model Ceramic Superconductors. By using Monte Carlo simulations it is shown that the aging disappears in the strong screening limit. In the weak screening regime, aging is present even at low temperatures. For intermediate values of the self-inductance, aging occurs in an intermediate temperature interval but is suppressed entirely at high and low temperatures. Our results are in good agreement with experiments.
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Chiral Glass Phase in Ceramic Superconductors
arXiv: Disordered Systems and Neural Networks, 1999Co-Authors: Hikaru KawamuraAbstract:A three-dimensional lattice of the Josephson junctions with a finite self-conductance is employed to model the Ceramic Superconductors. By Monte Carlo simulations it is shown that the chiral glass phase is stable in three dimensions even under the influence of screening. The nonlinear ac susceptibility and the compensation effect are also studied. The compensation effect is shown to be due to the existence of the chiral glass phase. In agreement with experiments, this effect is demonstrated to be present in the Ceramic Superconductors which show the paramagnetic Meissner effect.
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monte carlo studies of the ordering of Ceramic Superconductors chiral glass orbital glass and nonlinear susceptibilities
Physical Review B, 1996Co-Authors: Hikaru KawamuraAbstract:Static and dynamic properties of the intergranular ordering of Ceramic Superconductors are studied by Monte Carlo simulations on a three-dimensional lattice model of a Josephson-junction array with finite self-inductance. Both cases of d-wave and s-wave pairing symmetries are studied. In the case of d-wave Ceramics, intrinsic frustration effects combined with quenched randomness lead to the glassy behavior reminiscent of the spin glass even in zero magnetic field. It is found that the zero-field nonlinear susceptibility exhibits a negatively divergent behavior, suggesting the occurrence of a cooperative transition into an ordered state characterized by the random freezing of chirality or flux. In this ``chiral-glass'' state, global ${\mathit{Z}}_{2}$ time-reversal symmetry appears to be broken spontaneously with keeping the U(1) gauge symmetry. Dynamic simulations on the linear ac susceptibility suggest that d-wave Ceramics exhibits much stronger dissipation than s-wave Ceramics in the low-frequency regime. In the case of s-wave Ceramics, standard superconducting transitions with broken U(1) gauge symmetry occurs where nonlinear susceptibility exhibits only a very weak anomaly. Implications to experiments on high-${\mathit{T}}_{\mathit{c}}$ Ceramics are discussed. \textcopyright{} 1996 The American Physical Society.
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Nature of Orbital-Glass Transition in d-Wave Ceramic Superconductors
Journal of the Physical Society of Japan, 1995Co-Authors: Hikaru KawamuraAbstract:A close connection is pointed out between the orbital-glass state recently proposed for high- T c Ceramic Superconductors and the chiral-glass state identified in X Y spin glasses. Based on this analogy, the orbital-glass state is argued to be an equilibrium phase with broken reflection (charge-conjugation) symmetry, but not a true superconductor on long length and time scales. The transition to the normal state lies in the universality class of the 3 d Ising spin glass. It is predicted that the nonlinear susceptibility in the zero-field limit exhibits a negative divergence for d -wave Ceramics and a positive divergence for s -wave Ceramics.
M. Wurlitzer - One of the best experts on this subject based on the ideXlab platform.
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Inter- and intragranular irreversibility temperatures in high Tc Ceramic Superconductors
Superconductor Science and Technology, 1993Co-Authors: I.d. Luzyanin, S. L. Ginzburg, V.p. Khavronin, É. G. Tarovik, B. Lippold, J. Herrmann, H. Börner, M. WurlitzerAbstract:It is first demonstrated experimentally that there are two different irreversibility temperatures, Tirrcer and Tirrgr (Tirrcer(Tirrgr), in high-T Ceramic Superconductors of the compositions Bi1.6Pb0.3Sb0.1Sr2Ca2Cu2.8Oy and YBa2Cu4O8. At T(Tirrcer, both intragranular and intergranular irreversible currents are induced by pinning. When T)Tirrgr, there are no irreversible currents. It is found that Tirrgr(Tc for bismuth Ceramics and Tirrgr approximately Tc for YBa2Cu4O8.
T S Kayed - One of the best experts on this subject based on the ideXlab platform.
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effect of magnetic field and gamma irradiation on the electrical properties and structure of the tl based Ceramic Superconductors
Superconductor Science and Technology, 2000Co-Authors: H Ozkan, N M Gasanly, T S KayedAbstract:The voltage-current (V -I ) characteristics, critical temperatures and the critical currents of Tl2 Ba2 CaCu2 O8 (Tl-2212) and Tl2 Ba2 Ca2 Cu3 O10 (Tl-2223) Ceramic Superconductors were studied in magnetic fields up to 80 mT after several irradiations up to 100 MR. The effect of irradiation on the structure of these materials has also been studied. The normal state resistance increases by 20-30% with irradiation, most of the changes taking place in low doses up to 10 MR. The critical temperatures of Tl-2212 and Tl-2223 decrease by about 8 K up to 30 MR and approach the saturation values of 101 K and 113 K, respectively, with further increase of dose. For Tl-2212 in the 96-98 K temperature range the V -I behaviours become nearly ohmic under a dose of about 30 MR or in an external magnetic field of 20-30 mT. In the same temperature range the critical current decreases rapidly in low doses up to 10-25 MR; above that it decreases only slightly. For both materials, the positions and widths of the x-ray diffraction peaks almost remain the same but the peak intensities decrease by 10-40% with irradiation, the rate of decrease being higher in the 0-30 MR range. These observations indicate that drastic changes in the lattice do not take place with irradiation but substantial electronic excitations and point defects may be generated, at higher rate in low doses, to affect the concentration and arrangements of the carriers and the links between the grains.
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voltage current characteristics of the thallium based Ceramic Superconductors
Superconductor Science and Technology, 1999Co-Authors: H Ozkan, U Topal, N M Gasanly, B A Albiss, T S KayedAbstract:Voltage-current (V-I) characteristics of the Ceramic Tl2Ba2CaCu2O8 (Tl-2212) and Tl2Ba2Ca2Cu3O10 (Tl-2223) Superconductors were studied in magnetic fields up to 80 mT at different temperatures just below the critical temperature. The V-I data were fitted to a power law expression V = I(T,B) in which the exponential parameter is found to decrease rapidly with increase of temperature and magnetic field. In zero magnetic field the slopes of versus T graphs change drastically in a narrow temperature range in which decreases from about 3 to about 2. At temperatures below about 0.8-0.9 Tc the critical current Ic rapidly decreases with magnetic fields up to about 20 mT. This is followed by a more gradual change up to about 60 mT before Ic decreases rapidly to zero in magnetic fields higher than 80 mT. These features of the Tl-based Ceramic Superconductors are quite similar to those of superconducting tapes. We propose that the lattice anisotropy, preferred orientation and behaviours of the weak and strong links between the grains play an important role in this similarity.
I.d. Luzyanin - One of the best experts on this subject based on the ideXlab platform.
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Inter- and intragranular irreversibility temperatures in high Tc Ceramic Superconductors
Superconductor Science and Technology, 1993Co-Authors: I.d. Luzyanin, S. L. Ginzburg, V.p. Khavronin, É. G. Tarovik, B. Lippold, J. Herrmann, H. Börner, M. WurlitzerAbstract:It is first demonstrated experimentally that there are two different irreversibility temperatures, Tirrcer and Tirrgr (Tirrcer(Tirrgr), in high-T Ceramic Superconductors of the compositions Bi1.6Pb0.3Sb0.1Sr2Ca2Cu2.8Oy and YBa2Cu4O8. At T(Tirrcer, both intragranular and intergranular irreversible currents are induced by pinning. When T)Tirrgr, there are no irreversible currents. It is found that Tirrgr(Tc for bismuth Ceramics and Tirrgr approximately Tc for YBa2Cu4O8.