ENHANCED MICROWAVE-ABSORPTION NEAR TC IN MICRON-SIZE POWDERS OF CUPRATE SUPERCONDUCTORS

We report a systematic study of a large peak in the microwave losses near T(c) in micron-size powders of high-T(c) superconducting cuprates. It is demonstrated that the effect arises because all the grains do not have a single T(c). The onset of superconductivity in some particles enhances the RF field ''seen'' by their neighbors leading to a net increase in absorption. The temperature regime of enhanced loss spans the extrema of the transition temperatures.