Non-ohmicI-Vbehaviour in granular and high- superconductors

Abstract

Current-voltage measurements performed on granular YBa 2 Cu 3 O 7−δ and (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10 high-T c superconducting samples below their transition temperatures revealed a power law (V = αI β ) over a wide range of applied voltage. The exponent β decreases linearly with increasing temperature, deviating from linearity at temperature T nl lower than T c . Moreover the resistivity (ρ) exhibits a slope change in a log(ρ)-log(1 − T /T c ) plot at a temperature T * < T c . We argue that T nl and T * may reflect changes in the dynamics of the intergranular (or Josephson) vortices just below the superconducting transition temperatures.

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“…These results indicate that the superconducting phase still exists under 10 Oe up to 400 K. Additionally, the critical current value was not yet zero (7 mA) even at 400 K and 3000 Oe or more in Figure 1(e) and (f). Therefore, we judge that the critical temperature of LK-99 is over 400 K. Moreover, since LK-99 has a polycrystalline morphology shown in Figure 2, the non-uniform resistivity of the bulk samples can be explained as inter-grain boundaries, intergranular vortex flow, free vortex flow (18)(19)(20) of polycrystalline superconducting phase. The Josephson-like phenomenon (Figure S1(a) in supplementary materials) for the under-damped junction of superconductor-normal metal-superconductor (21,22) or Intergrain coupled superconductors (23) and the thermoelectric effect (24)(25)(26) of the inter-or intra-grain network(Figure S1(b) in supplementary materials) were also observed.…”