Field modulated microwave absorption and irreversibility line in [formula omitted] multilayers

Abstract

We describe field modulated microwave absorption measurements in two series of YBa 2Cu 3O 7 PrBa 2Cu 3O 7 multilayers: those with PrBa 2Cu 3O 7 thickness in the range ∼2.5 to ∼10 nm and with a fixed YBa 2Cu 3O 7 thickness of ∼10 nm and those with different resistivities of the PrBa 2Cu 3O 7 barrier with the same thickness of ∼2.5 nm for YBa 2Cu 3O 7 and PrBa 2Cu 3O 7 layers. The Fourier spectrum of the reflected microwave power reveals one fundamental frequency which appears at T c and even harmonics of the modulation field frequency f at lower temperatures. The determination of the irreversibility line near T c inferred from the vanishing of the nonlinear response signal at 2 f in the presence of superimposed d.c. and modulation fields is reported. A comparison with results obtained on YBa 2Cu 3O 7 thin films is also given.