Spectroscopic Observation of Bipolaronic Point Defects in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>Ba</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">K</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mi>BiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

Nishio, Toshiyuki; Ahmad, Javed; Uwe, Hiromoto

doi:10.1103/physrevlett.95.176403

Cited by 40 publications

(21 citation statements)

References 22 publications

(47 reference statements)

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“…There have been many studies of the metal-insulator transition at x = 0.3 in Ba 1−x K x BiO 3 and these have been interpreted in terms of bipolaron formation [73]. However, a more appealing interpretation of the Ba 1−x K x BiO 3 metalinsulator transition would be the onset of percolative metallic patches, as the "bipolaronic" infrared dopant peak appears to merge with the CDW band edge at x = 0.3, where T c is largest.…”

Section: Discussionmentioning

confidence: 99%

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

Phillips

2010

J Supercond Nov Magn

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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 .

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Section: Discussionmentioning

confidence: 99%

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

Phillips

2010

J Supercond Nov Magn

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“…These ceramic midinfrared data merely reinforce the large qualitative difference between layered ceramics (La 2−x Sr x CuO 4 ) and cubic Ba 1−x K x BiO 3 known from their phase diagrams. The former has a parabolic (nearly semicircular) T c ðxÞ, while the latter has a triangular T c ðxÞ, with a maximum T c at the metalinsulator transition and a normal BCS-type infrared spectrum with E g ∕kT c ¼ 3.2 (23), and a metal-insulator transition at x ¼ 0.3 in Ba 1−x K x BiO 3 , which has been interpreted in terms of bipolaron formation (24).…”

Section: Percolative Angular Gap Equationmentioning

confidence: 99%

Percolative theories of strongly disordered ceramic high-temperature superconductors

Phillips

2010

Proc. Natl. Acad. Sci. U.S.A.

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Optimally doped ceramic superconductors (cuprates, pnictides, etc.) exhibit transition temperatures T c much larger than strongly coupled metallic superconductors like Pb (T c ¼ 7.2 K, E g ∕kT c ¼ 4.5) and exhibit many universal features that appear to contradict the Bardeen, Cooper, and Schrieffer theory of superconductivity based on attractive electron-phonon pairing interactions. These complex materials are strongly disordered and contain several competing nanophases that cannot be described effectively by parameterized Hamiltonian models, yet their phase diagrams also exhibit many universal features in both the normal and superconductive states. Here we review the rapidly growing body of experimental results that suggest that these anomalously universal features are the result of marginal stabilities of the ceramic electronic and lattice structures. These dual marginal stabilities favor both electronic percolation of a dopant network and rigidity percolation of the deformed lattice network. This "double percolation" model has previously explained many features of the normal-state transport properties of these materials and is the only theory that has successfully predicted strict lowest upper bounds for T c in the cuprate and pnictide families. Here it is extended to include Coulomb correlations and percolative band narrowing, as well as an angular energy gap equation, which rationalizes angularly averaged gap∕T c ratios, and shows that these are similar to those of conventional strongly coupled superconductors. percolation | theoryA ll known microscopic theories of metallic superconductors are based on the isotropic Bardeen, Cooper, and Schrieffer (BCS) model of Cooper pairs formed by attractive electronphonon interactions that overwhelm repulsive Coulomb interactions, yet many features of electron-phonon interactions in the BCS theory that are confirmed in metals appear to be weak or absent in the infrared spectra of ceramic layered high temperature superconductors (HTSC) (1). The ceramics often exhibit multiple phases and must be doped to be not only superconductive but even metallic. By contrast layered undoped MgB 2 with T c ∼ 40 K is an "ideal" example of a metallic BCS crystalline superconductor where T c can be calculated quite accurately (2). When MgB 2 is substitutionally doped with ∼10% Al (on the Mg sites) or C (on the B sites), T c decreases drastically to ∼10 K (3). Many authors have invoked residual spin interactions in the doped state, left over from the magnetic undoped states, as a source of this difference (1). However, it has been known for a long time that electron-spin interactions (for instance, with magnetic impurities) drastically suppress T c by breaking S ¼ 0 Cooper pairs (4), and more generally that the insulating antiferromagnetic (AF) and metallic Cooper pair four-particle plaquette channels are completely independent (5). While ceramics often exhibit multiple phases, recently the data have shifted overwhelmingly in favor of phonon exchange as the only attractive interaction cor...

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“…In recent years, many efforts have been devoted to explore new superconducting materials and improving the preparation methods of existent superconductors [1][2][3][4]. As the first copper-free oxide superconductor with the transition temperature as high as 30 K, the Ba 1−x K x BiO 3 system has triggered extensive research in recent decades [5][6][7][8][9][10]. However, the synthesis routes of these oxides are not so convenient due to their poor thermal stability.…”

Section: Introductionmentioning

confidence: 99%

Hydrothermal synthesis of superconductors Ba1−xKxBiO3 and double perovskites Ba1−xKxBi1−yNayO3

Zhang

Huang

et al. 2011

Journal of Alloys and Compounds

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Spectroscopic Observation of Bipolaronic Point Defects inBa1−xKxBiO3

Cited by 40 publications

References 22 publications

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

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

Percolative theories of strongly disordered ceramic high-temperature superconductors

Hydrothermal synthesis of superconductors Ba1−xKxBiO3 and double perovskites Ba1−xKxBi1−yNayO3

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