Vortex Dynamics Of High-temperature Superconductors Research Articles

Vortex dynamics studies in pulsed magnetic fields

We have studied the vortex dynamics of High-Temperature Superconductors (HTS) in pulsed magnetic fields up to 50 T. Due to the very high sweep rates involved ( μ 0d H a/d t≈10 4 T/s), the induced current density j approaches the non-relaxed critical current density j c0. Turning the sweep rate during a high-field pulse makes it possible to vary the voltage criterion at which j is determined. Furthermore, the use of pulsed magnetic fields substantially increases the experimentally accessible region in the H– T phase diagram.

Vortex liquid properties in optimally doped and oxygen-deficient YBa 2Cu 3O 7− δ single crystals

The electrical anisotropy, γ=( m c / m ab ) 1/2, can easily be varied by changing the oxygen content in single crystals of YBa 2Cu 3O 7− δ (YBCO), thus making this system useful as a test system for vortex dynamics in high-temperature superconductors (HTSC). Here, some recent results are reviewed. Measurements of the c-axis resistivity with the magnetic field B∥ ab-plane is shown to be a powerful tool in studying vortex velocity correlations both parallel and perpendicular to the applied field. In optimally doped crystals, we find evidence that the in-plane vortex lattice melts at T m into a disentangled vortex liquid, which looses its correlation along the c-axis at a higher temperature T br> T m. For weakly disordered crystals and magnetic fields B∥ c-axis, a relation between the vortex glass line and the magnetic field dependence of the characteristic energy, U*, in the pinned vortex liquid is proposed. This approach is shown to give support to our idea of describing the vortex glass resistivity in the liquid regime by a modified glass correlation length, ξ g= ξ 0| k B T/ U 0−1| − ν , which depends on the average pinning energy, U 0, in the system [A. Rydh, Ö. Rapp, M. Andersson, Phys. Rev. Lett. 83 (1999) 1850].

Intrinsic and disorder-induced anisotropic vortex dynamics of high-temperature superconductors

The intrinsic and disorder-induced anisotropic vortex dynamics of high-temperature superconductors are investigated. Different universality classes of vortex phase transitions are found to be induced by different correlated static disorder for magnetic fields aligned with the disorder, whereas defect-independent vortex dynamics due to the intrinsic pinning of the layered structure are observed for fields parallel to the CuO2 planes.

Investigation of the current-induced nonlinear vortex dynamics in YBa2Cu3O7 single crystals using transport and transmittivity measurements

The current-induced nonlinear vortex dynamics of high-temperature superconductors are investigated in two YBa2Cu3O7 single crystals: one untwinned and the other with canted columnar defects. Both the electric transport properties and harmonic transmittivities demonstrate unique current-driven effects associated with the intrinsic pinning forH¯⊥ĉin layered superconductors, in contrast to the defect-dependent current-driven effects forH¯|ĉ.

High-Frequency Vortex Critical Dynamics of Superconducting Amorphous Mo3Si Films

The effects of static disorder on the vortex dynamics of type-II superconductors are investigated by comparing the high-frequency vortex response of superconducting amorphous Mo3Si (a- Mo3Si ) films with that of the high-temperature superconductors. We find that for a- Mo3Si films in the three-dimensional limit, the microwave vortex response near the second-order vortex-solid to vortex-liquid glass transitions is consistent with vortex critical relaxation, in contrast to the diffusion vortex dynamics in high-temperature superconductors at the same frequencies. The observation of microwave vortex critical dynamics in a- Mo3Si is attributed to the extremely disordered nature of the amorphous superconductors, which results in a much shorter-range vortex correlation and therefore a faster critical relaxation.

High-frequency vortex dynamics and dissipation of high-temperature superconductors.

The high-frequency vortex dynamics of high-temperature superconductors near the flux-line depinning threshold is investigated based on a thermally activated flux-flow (TAFF) model. Dissipation due to vortex motion driven by a microwave electromagnetic field is studied as a function of the frequency, temperature, dc magnetic field, and microwave power. The generalized TAFF model is also compared to the conventional flux-creep theory and is found qualitatively consistent.