Critical-state flux penetration and linear microwave vortex response in YBa2Cu3O7-delta

Article

关键词: LOWER CRITICAL FIELDS;    COUPLED-GRAIN MODEL;    MAGNETIC-FIELD;    THIN-FILMS;    II SUPERCONDUCTORS;    SURFACE IMPEDANCE;    GEOMETRICAL BARRIERS;    FREQUENCIES;    DEPENDENCE;    DYNAMICS;   

DOI  :  10.1103/PhysRevB.56.11989

来源: SCIE

【 摘 要 】

The vortex. contribution to the de magnetic field (H) dependence of the microwave surface impedance (Z) over tilde(s)(H)=R-s(H)+iX(s)(H) of YBa2Cu3O7-delta thin films was measured using suspended patterned resonators. (Z) over tilde(s)(H) is shown to be a direct measure of the flux density B(H) enabling a very precise test of models of flux penetration. Three regimes of field-dependent behavior were observed: (1) Initial flux penetration occurs on very low-field scales H-i(4.2 K)similar to 10 mT, (2) at moderate fields the flux penetration into the virgin state is in excellent agreement with calculations based upon the field-induced Bean critical state for thin-film geometry, parametrized by a field scale H-s(4.2 K)similar to J(c)d similar to 0.5 T, and (3) for very high fields H much greater than H-s, the flux density is uniform and the measurements enable direct determination of vortex parameters such as pinning force constants alpha(p) and vortex viscosity eta. However, hysteresis loops are in disagreement with the thin-film Bean model, and instead are governed by the low-field scale H-i, rather than by H-s. Geometric barriers are insufficient to account for the hysteresis loops. [S0163-1829(97)08641-4].

【 授权许可】

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