Microwave absorption in a Y1Ba2Cu3O7-x single crystal near the superconducting transition

Y1Ba2Cu3O7-x single crystals are investigated near T-c approximate to 92 K in fields 0<Hz less than or equal to 9 kOe using a modified ESR spectromete r. The temperature modulation method is used for the first time, together w ith the traditional magnetic modulation method, to detect microwave respons es in single crystals. Superconducting-transition peaks shifted relative to one another in temperature and differing in shape are observed in the temp erature dependence of the corresponding signals partial derivative R/partia l derivative H and partial derivative R/partial derivative T (R - microwave absorption). The evolution of these peaks as a function of the field and t he angle theta between H and the c axis of the single crystal is traced. It is shown that the difference in the temperature dependences of the derivat ives partial derivative R/partial derivative H and partial derivative R/par tial derivative T is due to the broadening of the superconducting transitio n characteristic of HTSCs. (C) 1999 American Institute of Physics. [S1063-7 834(99)00301-9].