Influence of twin planes inYBa2Cu3

Rinke J. Wijngaarden

¹

,

R. Griessen

²

,

J. A. Fendrich

³

et al.

Abstract

The effect of twin planes in YBa 2 Cu 3 O 7 on the superconducting current flow is investigated. A single crystal containing only two twin planes is studied magneto-optically up to 1 T. It is found that flux enters the crystal very easily along the twin planes, but that it does not leave the sample preferentially along the twin planes. The flux present in the twin planes reduces the flux penetration in adjacent regions of the sample. During flux penetration, the current density across the twin plane is about half of the current density in the rest of the sample. Due to this, the shielding current breaks up into several subloops. From a simulation follows that in a thin sample flux penetration is enhanced at inward pointing irregularities of the edge of the sample.

Dynamic vortex phases and pinning in superconductors with twin boundaries

“…This produces a pile-up effect leading to a higher density of vortices on one side of the twin in agreement with observations by several groups including, for example, Vlasko-Vlasov et al [10], Welp et al [12], and Wijngaarden et al [14]. At lower angles between the Lorentz force and the twin, simulations [17] show that the flux moves in channels along the twin boundary while some guided motion of vortices along the edge of the twin still occurs.…”

“…At lower angles between the Lorentz force and the twin, simulations [17] show that the flux moves in channels along the twin boundary while some guided motion of vortices along the edge of the twin still occurs. At the lowest angles the flux flows most easily along the twin with a number of vortices escaping from the twin and forming a flame pattern flux profile in agreement with magneto-optical experiments [9,10,18,14].…”

Modeling flux pinning in thin undoped and BaZrO3-doped YBCO films

“…5 On some orthorhombic substrates ͑such as NdGaO 3 ͒ the twins are oriented in one direction, but they are still there. 27 Since the twin boundaries channel the vortex motion along them and impede the motion across them, 28,29 it is obvious that the geometrical size and shape of the twin structure has an effect on J c . YBCO films grown on MgO have variation in the crystal lattice orientation ͓Fig.…”

Magneto-optical investigation of flux penetration in a superconducting ring

“…We use two types of measurements: ͑i͒ conventional magneto-optics between two crossed polarizers; the spatial variation of the perpendicular component of the local induction B z at the sample is visualized as an intensity pattern; from the intensity images, the local field H z is determined using the calibration Iϭb f (H z 2 ), where I is the intensity and b is a proportionality constant. 20 ͑ii͒ using our new magnetooptical image lock-in amplifier ͑MO-ILIA͒ setup, 15 the local magnetic field is measured directly as an output of the MO-ILIA. The second technique is a considerable improvement due to the intrinsic linearity in field, the direct measurement of the sign of the field, and the improved sensitivity at small magnetic fields.…”