Origin of the irreversibility line in thinYBa2Cu3O

Abstract

We report on measurements of the angular dependence of the irreversibility temperature T irr (θ) in Y Ba 2 Cu 3 O 7−δ thin films, defined by the onset of a third harmonic signal and measured by a miniature Hall probe. From the functional form of T irr (θ) we conclude that the origin of the irreversibility line in unirradiated films is a dynamic crossover from an unpinned to a pinned vortex liquid. In irradiated films the irreversibility temperature is determined by the trapping angle.

Interplay between two families of columnar defects inBi2Sr2CaCuHébert1, Perkins2, El-Salam3 et al. 2000Phys. Rev. B8010View full textAdd to dashboardCite

“…Note that similar results were obtained in YBCO crystals and thin films, 8,12,15 but no explanation was proposed. First of all, the absence of a peak cannot be ascribed merely to a 2D behavior of vortices, 42 for that would yield a ⌬M () independent of at fixed H c , in contrast to the strong angular dependence seen in Fig.…”

“…For the latter, in the case of two sets of tilted defects, the angular dependences of resistivity and of the magnetic properties are similar: maxima of current densities, 15,21,22 of H irr , 8,12 and minima of resistivity 19,20 are obtained when the magnetic field is applied along the mid-direction of the defects ͓i.e., along the c axis for defects tilted by Ϯ i from c ͑see, e.g., Ref. 15͒, or for example 10°from c for defects tilted by 5°a nd 15°͑Ref.…”

“…In YBCO, the efficiency of splay has been shown by means of magnetic [5][6][7][8][9][10][11][12][13][14] and transport measurements, [15][16][17][18][19][20] and several studies have already been devoted to the estimation of an optimal splay angle. 9,11,14,18 On the other hand, it has also been argued that splay might increase vortex creep in the case of large splay angles, 9 because defect crossings might favor vortex nucleation by locally lowering the pinning potential, but this is still controversial.…”

“…9,11,14,18 On the other hand, it has also been argued that splay might increase vortex creep in the case of large splay angles, 9 because defect crossings might favor vortex nucleation by locally lowering the pinning potential, but this is still controversial. 13 The angular dependence of the pinning properties of these splayed distributions has also been investigated, 8,12,15,[19][20][21][22] as will be described below.…”

Harmonic calculations and measurements of the irreversibility field using a vibrating sample magnetometer

“…Hence the interpretation of the parameters derived from resistive data can equally be in terms of giving the boundary for zero-resistance percolation in a highly disordered or inhomogeneous superconductor 46 or in terms of a transition from a pinned to unpinned vortex liquid. 47,48 To contribute to unravelling the complexity of magnetic phase diagrams, we suggest that measurements of B IRR and can be improved to give data closer to the ultimate sensitivity of the instrument rather than limited by the field inhomogeneity of the magnet.…”