Hard-Wired Dopant Networks and the Prediction of High Transition Temperatures in Ceramic Superconductors

Abstract

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 CuO 2 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 CuO 2 .

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

“…We totally agree with such considerations in the sense of the important role of disorder in superconductors with high T c on the verge of crystal lattice instability [73][74][75][76][77][78][79][80][81][82][83]. Nevertheless, it is questionable whether a simple one-parameter "master function" of [63,67] would be able to make quantitative and practically precise predictions of T c . As for the qualitative correctness of the dependence T c versus weighted number R of Pauling resonating valence bonds [63,67,84], it can be considered at least as a useful guideline in the superconductivity ocean.…”

“…It means that microscopic theories of superconductivity are incapable of describing specific materials precisely, although together they give an adequate overall picture. In this connection, the failure of the most sophisticated approaches to make any prediction of true or, at least "bare" T c , (provided that the corresponding T c -value is not known a priori) despite hundreds of existing superconductors with varying fascinating properties, forced Phillips [63] to reject all apparently first-principle continuum theories in favor of his own percolative filamentary theory of superconductivity [64][65][66][67] (see also the random attractive Hubbard model studies of superconductivity [68,69] and the analysis of competition between superconductivity and charge density waves studied in the framework of similar scenarios [70][71][72]). We totally agree with such considerations in the sense of the important role of disorder in superconductors with high T c on the verge of crystal lattice instability [73][74][75][76][77][78][79][80][81][82][83].…”

“…Nevertheless, it is questionable whether a simple one-parameter "master function" of [63,67] would be able to make quantitative and practically precise predictions of T c . As for the qualitative correctness of the dependence T c versus weighted number R of Pauling resonating valence bonds [63,67,84], it can be considered at least as a useful guideline in the superconductivity ocean. The phenomenological character of the master function (chemical trend diagram) T c ( R ) is an advantage rather than a shortcoming of this approach, as often happens in the physics of superconductors (see, e.g., more or less successful criteria of superconductivity with different extent of phenomenology [85][86][87][88][89][90][91][92][93][94][95][96][97][98]).…”

Correlation of structural, magnetic, and electronic transitions of a novel charge-gradientYBa2Cu3O∇xfilm

“…In the course of establishing this novel sample preparation route, we have also observed that the YBa 2 Cu 3 O ∇x film exhibits twin-free properties, i.e., behavior comparable to that observed for twin-free YBa 2 Cu 3 O x single crystals under uniaxial stress. We have also found new novel evidence furthering the already well established link between oxygen, electronic, and structural ordering [18][19][20]48,56,57 in the form of local oxygen content stabilization against the annealing thermal gradient at the p ≈ 1/7 level, and to a lesser extent at the p ≈ 1/8 level as well. We believe that the evolving electronic and structural nature of the YBa 2 Cu 3 O x films make them ideal for carrying out new novel experiments which could potentially discriminate TABLE I. c-axis length c(nm) calculated from x-ray data, inferred hole doping content p using Eq.…”

“…47,[52][53][54] (2b) The intrinsic instabilities within the lattice, and the percolative nature of the superconducting path which is embeded in a poor metallic background. [55][56][57] (3a) The highly correlated nature of electronic charge doping in the CuO 2 plane and oxygen ordering in the Cu-O chains noted above in Refs. [18 -20].…”