Investigation of stimulated dynamics of vortex matter in high-temperature superconductors

Abstract

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

Investigation of relaxation phenomena in high-temperature superconductors HoBa2Cu3O7−δ at the action of pulsed magnetic fields

“…3, does not change, but when this duration becomes of the order of the time for penetration of vortices into the sample and the creation of a vortex structure, then the aforementioned change of relaxation processes could principally appear. Namely, this situation when the duration x of magnetic pulses was larger than the time for Abrikosov vortex lattice creation x c , as described by us our previous work [19], where it was shown that the influence of one magnetic pulse h ≈ 400 Oe ( h H ) with duration 30 µs > x c was stepwisely decreased the τ rel moment and the relaxation process continued with the reduction of τ rel on a level as far as a new magnetic pulse similar the first one is not applied.…”

“…Just in this region, when ω 1 = ω 2 the torque τ , appeared to the uniformly rotating sample, is balanced by the countermoment τ p and τ fr . In particular, in the case of a continuously rotating sample with frequency ω 1 = ω 2 one could find similarly to [26,27] the expression for the total braking torque τ [19].…”

“…In work [19] it was also shown that a continuous action of the aforementioned pulses with a train frequency equal to 2.5 s −1 The results presented in Fig. 5 show that at durations of pulses of 20 µs, 30 µs and 40 µs the Abrikosov vortices penetrate into the superconductor.…”

“…1 [19,20]. In the experiments it is measured the rotation angle ϕ 2 of the sample depending on the angle of rotation of a torsion head ϕ 1 , transmitting the rotation to a sample by means of a suspension having a torsion stiffness of K ≈ 4 × 10 −1 [dyn cm].…”

Investigation of stimulated dynamics in strongly anisotropic high-temperature superconductors system Bi–Pb–Sr–Ca–Cu–O

“…For investigation it was used currentless mechanical method of Abrikosov vortex stimulated dynamics study by magnetic pulses revealing relaxation phenomena in vortex matter described in work [16]. This method is a development of currentless mechanical method of pinning investigations [17,18] and is based on pinning forces countermoments measurements and viscous friction, acting on a axially symmetrical superconducting sample in an outer (transverse) magnetic field.…”