Nonlinear microwave response of Bi-Sr-Ca-Cu-O single crystal at microwave frequencies

The third harmonic generation by monocrystalline Bi-Sr-Ca-Cu-O under the influence of high microwave power at frequency 9 GHz has been investigated. Two modes of operation have been found. For comparatively weak driving forces we observed that dc magnetic field significantly increased amplitude of the third harmonic hysteresis when the dc magnetic field was changed, and different amplitude of the third harmonic for zero- and nonzero-field cooled states. All these peculiarities could be explained in the framework of phenomenological Ginzburg-Landau theory if one takes into account the higher spatial derivatives of the order parameter. At strong driving forces we found only weak influence of dc magnetic field without any hysteresis. It probably indicates that the harmonic generation for these powers is the result of creating and destroying vortices by a high-frequency field.