In the presence of anisotropic pinning due to unidirected twins, the nonlinear vortex dynamics is discussed in terms of phenomenologically introduced anisotropic drag and pinning viscosities. The theoretical basis for experimental reconstruction of these viscosities is proposed. The nonlinear Ohm's law is derived. Assuming the anisotropic pinning alone (a-pinning model): a) new scaling relations for the anisotropic Hall conductivity are predicted; b) nonlinear guiding effects are discussed; c) specific current and angular behavior of current-voltage characteristics are analyzed.

The measurement of the complex impedance response and accompanied power absorption <$E P( omega )> in the radiofrequency and microwave ranges represents a most popular experimental method to investigate pinning mechanisms and the vortex dynamics in type-II superconductors. In the theory, the pinning potential (PP) well for a vortex must be a priori specified in order to subsequently analyze the measured data. We have theoretically solved the inverse problem at T = 0 K and exemplify how the coordinate dependence of a PP can be determined from a set of experimental curves <$EP( omega | j sub 0>) measured at subcritical dc currents <$E0~<<~j sub 0 ~<<~j sub c> under a small microwave excitation <$Ej sub 1 ~<< <<~j sub c> with frequency <$Eomega>. We furthermore elucidate how and why the depinning frequency <$Eomega sub p>, which separates the non-dissipative (quasi-adiabatic) and the dissipative (high-frequency) regimes of small vortex oscillations in the PP, is reduced with the increase of <$Ej sub 0>. The results can be directly applied to a wide range of conventional superconductors with a PP subjected to superimposed dc and small microwave ac currents at <$ET~<< <<~T sub c>.

Індекс рубрикатора НБУВ: В368.31

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Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 
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