•Juergen Halbritter
Forschungszentrum Karlsruhe, IMF 1, Postfach 3640, D-76021 Karlsruhe, Germany

The culprit of superconducting transport in HTS is asymmetry, and related to this, in-plane weak links degraded strongly shown by j_CJ << j_CP @ 4×10⁸ A/cm², by j_CJR_bn << D/e (sc energy gap) and by enhanced boundary resistance R_bn >> R_sh @ 10^-11 Wcm² (Sharvin resistance). The degradations are due to quasi two-dimensional metallic conduction in CuO-planes being separated by quasi-insulated blocking layers of thickness d^{^} ³ 0.8 nm driving a metal-insulator transition. Hence, any perturbation yields insulating plaques in the CuO-planes with plenty of localized states n_L (x, e) therein given by intrinsic and extrinsic interface relaxation. The resonant tunneling vie n_L describes quantitatively not only transport perpendicular to the planes and across external surfaces but also j_bn of in-plane weak links which converts in the superconducting state to the Josephson tunnel current j_cJ and to the normal leakage tunnel current j_bl. Consequences of the localized states n_L(x,e) as ïntrinsic defects" causing pair weakening, noise, j_bl-enhancements, j_cJ-reductions, electric Z^E and magnetic Z^H_res rf residual surface impedance are elaborated. By resonant tunneling via n_L @ 10²¹/cm states

j_CJR_bn @ D/eexp(- kd), j_CJR_bl² @ j_CJR_bn² ³ 10^-12 VWcm² and differences between artifical and natural junctions are quantified for the first time. Ways out of the ßurface chemistry dead lock" with its tunnel anomalies and residual losses are analyzed.