A. Dulčić

Mechanisms of Field-Dependent Microwave Absorption in High-Tc Ceramic Superconductors

New experimental features of the field-modulated microwave absorption in high-Tc ceramic superconductors are presented. The proposed model for the loss mechanism can explain the complicated field and temperature dependences of the absorption signals.

EPR detection of the flux distribution in ceramic high-Tc superconductors

Abstract EPR measurements were made on adsorbed diphenyl picrylhydrazil (DPPH) at the surface of a ceramic high- T c superconductor YBa 2 Cu 3 O 7 . A significant broadening of the EPR linewidth was observed below the superconducting transition temperature T c . It is interpreted as a broadening due to the spatial distribution of the flux in the superconducting mixed state which is developed at the resonant magnetic field H 0 (H Cl ⪡ H 0 ⪡ H C2 ). The penetration depth of the magnetic field can be determined by this simple technique.

Microwave Study of Josephson Junctions in Gd-Ba-Cu-O Compounds

By studying the variation of the microwave absorption of superconductive GdBa2Cu3O9-y samples with an ESR apparatus, we have detected the influence of the magnetic field on the intergrain Josephson currents on the surface of the sample. The onset of superconductivity is easily detectable as a sharp signal rise. The observed evolution of the signal intensity below Tc is a useful indicator of the improvement of the superconducting properties of the sample. Quenched nonsuperconductive samples showed no signal at all.

Effects of alternating magnetic fields on the microwave absorption in ceramic high-Tc superconductors

Abstract Microwave absorption in ceramic high-Tc superconductors shows a complex response to applied d.c. and a.c. magnetic fields. In the total absorption signal, one can identify a component which is due to the modulation of the magnetic flux through the sample, and components which depend on the boundary current.

Comparison of direct and modulated microwave magnetoresistance in ceramic and single crystal YBa2Cu3O7−δ

Abstract A comparative study of microwave absorption in single crystals and ceramic samples of YBa 2 Cu 3 O 7−δ has made it possible to distinghuish the processes in the bulk from those in the intergranular medium. The origin of various types of hysteresis in direct and modulated absorption singnals is clarified. The appearance of the modulation-dependent hysteresis is shown to be an evidence of anharmonicity in the pinning potential.

Field-modulated microwave absorption in granular superconductors: First and second harmonic signals

Abstract Field-modulated microwave absorption in granular superconductors is analyzed within the weak link model. The signals are calculated for various modulation amplitudes, both for the first and the second harmonic detection. The calculation signal shapes are in good agreement with experimental results.

Microwave response of thin niobium films under perpendicular static magnetic fields

The microwave response of high quality niobium films in a perpendicular static magnetic field has been investigated. The complex frequency shift was measured up to the upper critical fields. The data have been analyzed by the effective conductivity model for the type-II superconductors in the mixed state. This model is found to yield consistent results for the coherence lengths in high-

An ac method for the precise measurement of Q-factor and resonance frequency of a microwave cavity

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Decoupled CuO 2 and RuO 2 layers in superconducting and magnetically ordered RuSr 2 GdCu 2 O 8

superconducting samples, and can be used with high-temperature superconductors even at temperatures much below

Transport and microwave study of superconducting and magnetic RuSr 2 EuCu 2 O 8

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