High Frequency Transport Properties of YBCO: Extrinsic Versus Intrinsic d-Wave Properties

Abstract

In good superconducting YBCO films, the surface impedance Z(T,ω,B)=Zint(T,ωB)+Zres(T,ωB) is dominated for T T c/2 and B∼0 by intrinsic properties, which are difficult to improve. Below T c/2, Z res usually dominates over Z, and below 0.9 T c, Z(T,ω,B) increases with field, both are, up till now, explained by extrinsic properties related to extrinsic and intrinsic surfaces. The latter are named weak or strong links (WSL), into which around B c1J for ω0 J » ω0 A Josephson fluxons (JF) enter, where Bc1J « Bc1 holds with Bc1 the lower critical field of Abrikosov fluxon (AF) with ω0 A ∼ MHz their nucleation or pinning frequency. Below fields ≲B C1 and below the pinning or nucleation frequency ω0 J ∼ THz hysteresis losses increase Z=R+iX nonlinearly with r(T,ω)=δ X/δ R∼2 with the surface resistance R and the surface reactance X. The nonlinearities decrease toward B c1J to (small) oscillation of JF yielding r(T,ω) δ ω0 J (T)/ω . Those Z nonlinearities yield harmonics or intermodulation products IMD(T). Below B c1J new types of nonlinearities relate to d-wave properties of HTS. Either nonlinear Meissner effect (NME) and anomalous Meissner effect (AME) at internal or external surfaces are proposed with r ≫ 1, observed by harmonic generation and by specific IMD(T, B) dependencies being identified recently. New developments in theory and experiment and procedures to separate extrinsic from intrinsic properties will be analyzed.