Quasi-One-Dimensional Intermittent Flux Behavior in Superconducting Films

Abstract

Intermittent filamentary dynamics of the vortex matter in superconductors is found in films of YBa 2 Cu 3 O 7-deposited on tilted substrates. Deposition of this material on such substrates creates parallel channels of easy flux penetration when a magnetic field is applied perpendicular to the film. As the applied field is gradually increased, magneto-optical imaging reveals that flux penetrates via numerous quasi-one-dimensional jumps. The distribution of flux avalanche sizes follows a power law, and data collapse is obtained by finite-size scaling, with the depth of the flux front used as crossover length. The intermittent behavior shows no threshold value in the applied field, in contrast to conventional flux jumping. The results strongly suggest that the quasi-one-dimensional flux jumps are of a different nature than the thermomagnetic dendritic (branching) avalanches that are commonly found in superconducting films. Since the prediction of a regular vortex lattice in type-II superconductors [1], a wide variety of vortex systems has been thoroughly investigated [2,3]. The pronounced dependencies of the range and strength of the vortex-vortex interaction on temperature and magnetic field make the vortex matter a unique, tunable model system for probing the statistical properties of interacting systems. The behavior of the vortex matter is to a large extent also determined by its interaction with quenched disorder in the material, i.e., with microscopic defects that pin the vortices and therefore serve as pinning centers in the superconductor. The interplay between the pinning forces and the driving Lorentz force leads to formation of a metastable critical state [4], where the current density has a critical magnitude, j c , which corresponds to the maximal nondissipative current density.In films of YBa 2 Cu 3 O 7-(YBCO) grown epitaxially, i.e., with proper matching of crystal lattice parameters, on a substrate slightly tilted from a major crystal plane (vicinal films), self-organized arrays of planar defects (antiphase boundaries) are formed with a typical period of 2-5 nm [5]. The terrace structure of the surface is characterized by steps that are a few Å ngströms in height, and the steps provide well-oriented seeding sites for growth along the main axis (c axis) of the overlying YBCO film. Films grown on substrates with a tilt angle of close to 10 have better grain alignment and improved current-carrying ability [5,6]. There has been considerable interest in such films due to their potential application in Josephsonjunction design [7][8][9], in particular for highly sensitive detectors of electromagnetic radiation.The growth of YBCO films on tilted substrates is also known to produce planar defects, which become channels for easy vortex motion [5,6,10]. These channels are separated by 5-10 m and run parallel to the terrace structure, causing considerable anisotropy in both the flux penetration and the effective critical current. At low temperatures, where the anisotropy is most pronounced, the vortices are es...

Characterization of <inline-formula> <tex-math notation="LaTeX">${YBa}_{2}{Cu}_{3}{O}_{7-\delta}$</tex-math> </inline-formula> Films With Various Porous Structures Grown by Metalorganic Decomposition Route

“…In Ref. [53], such penetration was observed in an YBCO film grown on a 14 • miscut NdGaO 3 substrate, and a power law was found for avalanche length distribution. Finite-size scaling and self-ordered criticality (SOC) were observed as well.…”

“…There is a certain amount of heating, but this is a non-dominant factor. In thin-film superconductors, they commonly appear as thin needle-like formations abruptly entering the sample from the edges [53]. Unlike thermomagnetic avalanches, they do not propagate beyond the critical state-like flux front, and their appearance does not seem to have threshold values for temperature or applied magnetic field.…”

Thermo-magnetic stability of superconducting films controlled by nano-morphology

“…30,31 However, unlike YBCO films, which had a well defined quasi periodic structure of planar defects, which gave rise to in-plane anisotropy of j c and channeling of vortices, NbN films are isotropic. The origin of such an ordering in isotropic NbN samples is not yet fully understood.…”

Scaling Behavior of Quasi-One-Dimensional Vortex Avalanches in Superconducting Films

“…Both kinds of avalanches can occur in the same sample [28,29]. There is extensive experimental and numerical evidence that under some conditions, quantities measuring the size of dynamically driven vortex avalanches are distributed according to power-laws, and may also exibit finite-size scaling [3,24,25,30,32]. For a recent review of SOC experiments in granular media and superconductors, see ref.…”