G. B. Teitel'Baum

Critical state of an YBa2Cu3Ox strip in a perpendicular magnetic field as revealed by a scanning ESR probe

Abstract The distribution of a magnetic field in a superconducting sample is studied by a scanning ESR microprobe. The main attention is focused to the penetration of a perpendicular magnetic field into an YBaCuO single crystal strip. The field profile in the interior of the sample is mapped from the data on the ESR-signal shift of the spin probe measured at different points over the plane surface. The penetration of the magnetic flux is shown to be delayed and this gives rise to the formation of steep fronts in the profile of the field near the center of the strip. The profile observed is highly dependent on the magnetic history. The demagnetizing effects and the distribution of the current are discussed. The analysis of the experimental data obtained gives evidence that the critical state picture differs considerably from the well known Bean model.

The critical state of superconducting strip in perpendicular magnetic field as revealed by moving ESR-probe

Abstract The new procedure of the magnetic field mapping with the help of ESR microprobe scanning over the surface is applied for investigation of the perpendicular magnetic field profile in the superconducting YBa 2 Cu 3 O x single crystal strip.

The manifestation of vortex-glass state in the microwave absorption of high-Tc superconductors

Abstract The studies of the flux lattice dynamics via the microwave absorption measurements with the help of ESR spectrometer are presented. For low temperatures the nonlinear dependence of the absorbed power on the input microwave power is discovered. The analysis of this phenomenon in terms of the collective creep theory gives evidence, that the flux lattice is frozen in a vortex-glass state.

The collective nature of a flux creep in high-T c superconductor YBa2Cu3O x as observed in microwave absorption experiments

Studies of the flux lattice dynamics via microwave absorption measurements with the help of an ESR spectrometer are presented. The experiments give evidence that for the temperatures below 35 K the absorbed power depends on the input microwave power in a non-linear way. For the case of absorption due to the motion of vortexes via thermally activated flux creep this corresponds to the dependence of the activation barrier on the current density. The measurements lead to the conclusion, that the activation barrier should grow with decreasing current. Fitting of the expression for the dissipated power obtained in terms of the collective creep theory to the obtained experimental data enable us to determine the character of pinning and creep at small amplitudes of the external exciting current. The obtained numerical values give evidence that the flux lattice is frozen in a vortex-glass state and in the limit of zero current the resistance at finite temperatures vanishes.

The effect of flux kinetics in the microwave absorption of YBaCuO single crystals

Abstract The time dependent anomalies of the microwave absorption due to the trapped magnetic flux are studied with the help of standard EPR spectrometer. The displacement of the observed extremum is described in terms of flux creep.