Microwave absorption studies on high-Tc superconductors and related materials VI-non-resonant microwave absorption in ultra-thin Bi-Sr-Ca-Cu-O films

This paper reports that non-resonant microwave absorption (NRMA) studies have been done for Bi-Sr-Ca-Cu-O (BSCCO) films with thicknesses of 30 Angstrom and 15 Angstrom fabricated on MgO substrate by MOCVD. For the latter two kinds of samples have been fabricated: BSCCO/MgO and BiOxBSCCO/MgO. NRMA signals have been detected up to about 70-75 K for all the samples. The lower critical magnetic field Hcl* of the 30 Angstrom film was severely increased by the application of a magnetic field of several kGauss, whereas it is almost unaffected in the case of 15 Angstrom films. Hcl* increases but the signal intensity decreases with increasing temperature for all the 30 Angstrom and 15 Angstrom samples. The temperature dependence of the intensity is quite different form that of thicker films (100 Angstrom and 350 Angstrom), in which the intensity vs. temperature relation has a peak (or peaks) at particular temperature(s)