Resistive transition anisotropy in superconducting granular ceramics: Interplay of effective medium approximation and percolation

Abstract

The resistive transition (T,H) in granular high-T c superconductors is described by a combination of the effective-medium approximation for anisotropic mixtures with the percolation theory. We found a single parameter accounting for both the structural anisotropy as well as for the intrinsic resistivity anisotropy of a single grain. We obtained a direct ͑no fitting parameters͒ estimate of the superconducting volume fraction f as a function of temperature, as well as of the percolation threshold f p and of the zero-resisitivity threshold f 0 . The model describes successfully the experimental (T,H) dependence at different relative directions of the c axis, the current j and the magnetic field H in Bi 2 Sr 2 CaCu 2 O 8Ϫx ceramics. We provided estimates for the value of the Josephson critical current between grains. The latter proves to be strongly suppressed even by weak magnetic fields HϽ750 Oe. This results in the appearance of the field-induced excess resistivity ⌬ that obeys the dependence 1/⌬Ӎ1ϩH /H, where H is the characteristic field trapped by a single Josephson contact.

Sonochemical modification of the superconducting properties of MgB2

“…. Controlled modification of the pinning properties of bulk granular superconductors is an active area of applied and fundamental research [1][2][3][4][5][6][7][8] . Doping with different metals 9,10 , variation of stoichiometry 11 and nonsuperconducting phase precipitation 12 are recent examples of the chemical tuning of superconducting materials.…”

Manipulating the optical transparency of anisotropic metamaterials with magnetic field and liquid crystals: influence of the nanostructures shape

“…The Effective Medium Approximation 33,51,52,56,[64][65][66][67][68] (as well as Clausius-Mossotti approximation) used above takes into account the shapes of the islands (through their depolarization factor n) and their sizes (through their volume fraction p 1 ) but does not take into account the distances between the islands. In order to take into account the latter we propose to make a coordinate transformation x =ĝ(x) · x, which transforms space in such a way that the distances between the inclusions become the same (see top of Fig.…”

Magnetoresistive effect in bulk composites 1-2-3 YBCO + CuO and 1-2-3 YBCO + BaPb1 xSnxO3and their application as magnetic field sensors at 77 K

“…The physical mechanism of the MR effect of polycrystalline HTSC has been discussed in the literature (see, for example, [1,3,5,6,[8][9][10][11][12][13][14][15][16]) and can briefly be considered as follows. It is well known that the resistive state of granular HTSCs is governed by intergrain boundaries which are weak links of Josephson type.…”

“…The possible practical aspects of the application of bulk high-T C superconductors (HTSCs) as magnetic field sensors were pointed out soon after the discovery of high-temperature superconductivity [1,2]. Polycrystalline HTSCs exhibit large magnetoresistance in weak magnetic fields (tens of oersteds) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. This effect can be used in devices that demand a sensitive electrical response for a weak magnetic field.…”