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Effect of oscillations of the vibration amplitude of cylindrical sample suspended by a thin elastic thread and vibrating in a transverse magnetic field and containing 2D quasi-two-dimensional vortices (pancakes), was observed in the strongly anisotropic high-T c superconductor of Bi 1.7 P b 0.3 Sr 2 Ca 2 Cu 3 O y system.

INTRODUCTION.Investigation of vortex state stimulated dynamics in high-temperature superconductors (HTSC) is one of the most important problems from the point of view of practical applications in the new generation of electronic devices operating on the basis of HTSC materials, as well as, from the point of view of fundamental problems connected with hightemperature superconductivity [1]. It is clear that vortex states in superconductors are complicated and multiform, but they are exceptionally important for understanding the behavior of high-temperature superconductors in electromagnetic fields and under the current loads [2]. The critical temperature T c of the superconducting transition of HTSC cuprates is so high that they remain superconductive at temperatures, at which the thermal fluctuations play a noticeable role, as their energy become comparable with the elastic energy of vortices and also with the pinning energy [3]. It creates prerequisites for phase transitions [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In the type-II HTSC superconductors the number of vortices, "particles" in the vortex matter may be changed in a very wide range, several orders of magnitude by varying the magnetic field, B. As the interaction between the vortices is changed, thermal fluctuations in the HTSC vortex matter can be observed in a very wide temperature interval, on the B-T phase diagram. This gives a good possibility to study the disordered media -one of the central problems of condensed state physics. The investigation of vortex matter dynamics is of particularly topical interest in the case of HTSCs, which, because of their high critical temperatures and layered structure are characterized by a much higher mobility of the vortex lattice, as compared with the ordinary type-II superconductors, which is hampered by pinning connected with various defects of the crystal structure. These defects are the pinning centers that prevent the flow of magnetic flux and the energy dissipation, accompanying it. In the strongly anisotropic high-temperature superconductors, as it was shown in recent works [16][17][18], the critical current at the transition of 3D vortices in the quasi-two-dimensional 2D vortices can be sharply increased, making such anisotropic high-temperature superconductors, e.g. BiPbSrCaCuO system, useful for technical applications. Furthermore, the upper critical field H c2 , at which the superconductivity in these materials is

The investigation of temperature dependence of damping and period of vibrations of HTSC superconductive cylinder of Bi-Pb-Sr-Ca-Cu-O system suspended by a thin elastic thread and performing axialtorsional vibrations in a magnetic field at temperatures above the critical one for the main phase T c =107 K were carried out. It was observed some "chaos" temperature region in the temperature interval 107-138 K, where it is seen separate ripples of dissipation and oscillation frequency. It is assumed that the "chaos" region could point to a possibility of existence of other magnetic and more high-temperature phases as single islands in a normal materials matrix.

A mechanical method to investigate the stimulated Abrikosov vortex dynamics in superconductors has been used. We found out that pulsed magnetic fields change the path of relaxation processes taking place in vortex matter. The study of the influence of magnetic pulses differing in their durations and amplitudes on the vortex system of the isotropic high-temperature superconductor system HoBa 2 Cu 3 O 7−δ showed the presence of a threshold phenomena. Short duration pulses do not change the path of relaxation processes taking place in vortex matter. When the duration of pulses exceeds some critical value (threshold), then their influence changes the path of relaxation process which is revealed by a stepwise change of the relaxing mechanical moment τ rel . These investigations showed that the time for formatting of the Abrikosov vortex lattice in HoBa 2 Cu 3 O 7−δ is of the order of 20 µs which exceeds by one order of magnitude the time necessary for formation of a single vortex observed in type II superconductors.