Formation of High Temperature Superconducting Balls

Abstract

High-T c superconducting particles of mm size in a strong electric field bind themselves together to form macroscopic balls in milliseconds. Each ball holds over 10 6 particles and bounces between the electrodes without losing any. The ball formation is a result of superconductivity. As the c-axis coherence length is shorter than the Thomas-Fermi screening length, the electric field produced by the charged surface layer turns off the coupling between the interlayers. This loss of Josephson energy becomes a positive surface energy induced by the charged surface layer, the minimization of which leads to the balls. PACS numbers: 74.80.Bj, 68.10.Cr, 83.80.Gv In nature, there are very few cases where granular particles could aggregate together by themselves to form a round ball. Application of an electric field further destroys space's isotropy. Therefore, it is against common sense that an electric field could drive high-T c superconducting (HTSC) particles together to form a round ball. However, this is our finding, which reveals a new property of high temperature superconductivity [1,2]. Moreover, this effect may be used to produce superconducting films on a solid substrate, leading to applications.The particles used in our experiment, YBa 2 Cu 3 O 72x (99.99% purity), NdBa 2 Cu 3 O x (99.9% purity), Bi 2 Sr 2 CaCu 2 O 81x (99.9% purity), and YbBa 2 Cu 3 O x (99.9% purity) were provided by Superconductive Components, Inc. (SCI), Columbus, OH. As shown in Fig. 1, the particle size is 1 2 mm. They were prepared either by a solid state method [3] or the Sandia Chemical Preparation [4]. One batch of YBa 2 Cu 3 O 7 granulated by us has a particle size of 4 5 mm. The superconductivity properties of individual particles were carefully studied by

Electrorheological Fluids

“…High-T c superconducting particles, such as YBa 2 Cu 3 O 7±x , NdBa 2 Cu 3 O x and YbBa 2 Cu 3 O x , and Bi 2 Sr 2 CaCu 2 O 8+x , have been found to form the fibrillated structure at room temperature in silicone oil, [86] indicating that they also have the ER effect. A macroscopic ball of diameter 0.25 mm is formed in milliseconds if superconducting particles of size 1±2 lm are dispersed in liquid nitrogen under an electric field of 0.8 kV/ mm.…”

Electrodynamics in superconductors explained by Proca equations

“…Jenks et al 7 performed such measurements on an YBCO High-T c superconductor and reported that the penetration depth down to T c was decreasing with temperature as expected from the Thomas-Fermi theory, but once the YBCO was superconductive, the electric field penetration depth increased again with temperature. Tao et al [8][9][10] recently observed the formation of balls when low and High-Tc superconducting particles were exposed to a strong electric field. In their analysis, they had to assume that the electric field penetration depth is at least an order of magnitude higher than the Thomas-Fermi length 9 .…”

Geometric treatment of electromagnetic phenomena in conducting materials: variational principles

“…This fits many experimental observations, including the influence of electrostatic fields on superconductors [7]. However, accounting for other classical [11] and very recent experiments [9], such proposal has been generalized to J = Ξ · A + Ω, with Ξ a (1, 1) tensor.…”

“…Essentially, and inspired in the principle of Lorentz covariance, when the electric and magnetic fields are treated at the same level, one predicts both electrostatic and magnetostatic field expulsion with a common penetration depth λ [3,4,5]. This formulation has been used [6] as a basis for explaining the so-called Tao Effect, an intriguing experimental observation, in which superconducting microparticles aggregate into balls in the presence of electrostatic fields [7]. However, both theoretical objections [8] as well as experimental results [9] raise concerns on the universality of the common λ treatment.…”