AC magnetic response of superconducting YBa2Cu3O7/PrBa2Cu3O7 superlattices

Abstract

Vortex activation energy U AC in the critical-state related AC magnetic response of superconductors (appearing in the vicinity of the DC irreversibility line) takes large values, as often reported, which is not yet understood. This behavior is essentially different from that of the vortex-creep activation energy at long relaxation time scales, and may become important for AC applications of superconductors. To elucidate this aspect, we investigated the AC signal of almost decoupled

Vortex dynamics driven by AC magnetic field in YBCO thin films with complex pinning structures

“…In summary we propose a practical formula for the determination of the induced current during AC susceptibility measurements at T>T p and the characteristic pining energy obtained from both E(J) characteristics and J(t=1/f ) dependence at short time scale was U c (85.5 K)≈900 K. It was found that, for H dc = 2 kOe, the flux velocity during AC measurements is v=0.3 cm s −1 and only 1 nm s −1 in DC relaxation measurements. Thus, the thermal smearing of the potential walls is reduced in AC experiments (as described in [24]) and the obtained U c is always higher than U c determined from DC magnetic measurements. Also, the dynamic critical current J d induced for AC driven forces at depinning frequencies was experimentally obtained by measuring m′ and m ″ as a function of T, for different f, h ac and H dc .…”

Vortex activation energy in the AC magnetic response of superconducting YBa2Cu3O7thin films with complex pinning structures

“…With J d ∼4×10 5 A cm −2 , and J=J p =J d , the above relation supplies U AC ∼2×10 3 K, which accounts for the order of magnitude of U AC just below the IL at μ 0 H DC =0.2 T. Estimated as above, L eff may introduce significant errors in the calculated U AC . For this reason, we have recently investigated the AC magnetic response of almost-decoupled YBa 2 Cu 3 O 7 /PrBa 2 Cu 3 O 7 superlattices [41], where the thickness of YBCO offers a precise measure of L eff [42], obtaining a good agreement between the determined and calculated U AC .…”