Field modulated microwave absorption in YBa2Cu3O7/PrBa2Cu3O7 multilayers

We describe field modulated microwave absorption measurements on YBa2Cu3O7/PrBa2Cu3O7 multilayers with PrBa2Cu3O7 thickness in the range 2.5 to 10 nm and with a fixed YBa2Cu3O7 thickness of 10 nm. The Fourier spectrum of the reflected microwave power reveals one fundamental frequency which appears at Tc and even harmonics of the modulation field frequency ω at lower temperatures. The determination of the irreversibility line near Tc for different values of the PrBa2Cu3O7 thickness and inferred from the vanishing of the nonlinear response signal at 2 ω in the presence of superimposed dc and modulation fields is reported.