Two-dimensional and three-dimensional vortex lattice dynamics inDyBa2Cu3

Abstract

Vortex dynamics is studied in coupled multilayer structures, containing N 24-A-thick DyBa&Cu307 layers, each separated from the next by 96 A of (Y& "Pr")Ba2Cu307 (x =0. 4, 0.55). When the magnetic field is parallel to the c axis, we find that the activation energy U for 6ux motion increases linearly with the number of superconducting layers N in the structure for N & 3. This linear increase is the result of the coupled motion of pancake vortices belonging to de'erent DyBa2Cu307 layers. For larger N samples the activation energy saturates meaning that the vortex lattice is turning three dimensional. In contrast to samples whose vortex lattice is purely two dimensional and for which we find the activation energy for flux motion proportional to log, oE, samples in these series show a crossover to a power-law behavior, U=8, at a magnetic field H which decreases as N increases. I. IN. rRODUc:rxONThe H-T phase diagram of high-T, superconductors is one of the most fascinating and discussed aspects of these materials. Questions related to, for instance, thermal fiuctuations, the irreversibility line, or the existence of a vortex glass and/or a melting transition are still under debate. ' For several of these problems the dimensionality of the vortex lattice is a crucial parameter and predictions concerning the low-temperature phase of the vortex lattice have been made depending on its dimensionality. High-T, superlattices may be a useful tool to address some of these questions. The main advantage of these arti6cial structures is to provide a way to control and modify the vortex lattice parameters and, in particular, its dimensionality, allowing to track the effects of such changes on specific physical properties. Recently, s s we studied extensively the flux dynamics in YBaxCu307/PrBa2Cu307 (YBCO/PrBCO) superlattices.In these superlattices the thickness of "insulating" PrBCO, 96 A, is sufficien to essentially decouple the superconducting layers (as will be discussed below, magnetic coupling is irrelevant to this study}. The main result was that the activation energy for Aux motion U, in the regime of linear I-V characteristics, is proportional to the YBCO thickness in the multilayers for d-YBCO & 300 A, and has a logarithmic field dependence, for H parallel to the c axis. The scaling of the activation energy with the YBCO thickness refiects the absence of interaction between pancake vortices of difFerent superconducting layers. The correlation length L, involved in this activated motion of vortices is found to be about 400 A implying a two-dimensional (2D) vortex lattice in YBCO layers thinner than 400 A. The logarithmic field dependence of the activation energy found in YBCO/PrBCO multilayers as well as in thin YBCO layers has its origin in the 2D nature of the vortex lattice as discussed below. Notice here that the correlation length L"as de6ned and measured in this work is not identical to the Larkin-Ovchinnikov collective pinning correlation length, although certainly related to it. Ongoing measurements of creep at l...

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“…For a 2D vortex lattice U͑H͒ ϳ 2 lnH [18], implying a power-law field dependence of s J aH 2n with n͑T ͒ ഠ 1 1 U͞T . The low-field s ab ͞s c is indeed nearly linear in H (inset in Fig.…”

Unusual Vortex Dynamics in Nb–a-Si Multilayers with Strong Interlayer Coupling

“…The discovery of superconductivity in the anisotropic high-T c oxides has triggered renewed interest in investigations of other naturally anisotropic [1] superconductors as well as artificially layered stacks [2][3][4][5][6][7][8][9] regarding, e.g., the dimensionality of the flux dynamics. Recently, some very interesting, nonlinear, vortex dynamics were reported [1] in NbSe 2 which has extremely weak pinning.…”

Variation of c-axis correlation on vortex pinning by ab-plane non-superconducting layers in YBa2Cu3O7 films

“…The dimensional crossover from 2 dimensional (2D) vortex to 3D one was discussed in YBCO/ PrBCO MLs by many researchers. [23][24][25] In the YBCO/PrBCO MLs with YBCO layer thickness smaller than 24 nm, 2D vortex behavior was observed by Brunner et al 23 The YBCO þ BSO/PrBCO (15 nm/3 nm) ML exhibits 2D vortex as shown in inset of Fig. 7(c).…”

“…Vortex behavior in YBCO/PrBa 2 Cu 3 O 7 (PrBCO) multilayer films (MLs) was previously investigated by many researchers. [23][24][25] However, since these studies focused mainly on vortex dimensionality, the mechanism of compound pinning and variation of three dimensional (3D) vortex phases (especially the Bose glass) were not discussed. In the present study, to understand the vortex pinning of the multiple-defects, YBCO þ BSO/PrBCO MLs were fabricated, where BSO nanorods grew along the c-axis and PrBCO formed nonsuperconducting layers parallel to the ab-plane, respectively.…”