Field-Modulated Microwave Absorption in Granular Superconductors: First and Second Harmonic Signals
The dependence of the microwave absorption on the applied magnetic fields was extensively studied in high-Tc copper-oxide superconductors. The first harmonic lock-in detection of the modulated absorption did not result in the expected first derivative signals (1-3]. The second harmonic lock-in detection of the modulated absorption was also reported (4). In contrast to the first harmonic signals, the second harmonic signals showed no hysteresis at low modulation amplitudes, while a small hysteresis appeared at large modulation amplitudes.