Dynamics of stripe patterns in type-I superconductors subject to a rotating field

The evolution of stripe patterns in type-I superconductors subject to a rotating in-plane magnetic field is investigated magneto-optically. The experimental results reveal a very rich and interesting behavior of the patterns. For small rotation angles, a small parallel displacement of the main part of the stripes and a corotation of their very ends are observed. For larger angles, small sideward protrusions develop, which then generate a zigzag instability, ultimately leading to a breaking of stripes into smaller segments. The short segments then start to corotate with the applied field although they lag behind by approximately 10°. Very interestingly, if the rotation is continued, reconnection of segments into longer stripes also takes place. These observations demonstrate the importance of pinning in type-I superconductors.

Figure 1

Schematic of sample and magnetic-field configuration. $H$ is the applied magnetic-field vector, $H_{xy}$ is the projection of $H$ onto the plane of the superconductor.

Figure 2

Sequence of images for different directions of the applied in-plane field, $H_{xy}$. (a) $\theta =0°$, (b) $\theta =15°$, (c) $\theta =30°$, (d) $\theta =45°$. The straight lines on the lower left indicate the direction of $H_{xy}$. White (black) corresponds to superconducting (normal) regions and the scale bar corresponds to $0.5\mathrm{mm}$.

Figure 3

Left panel: overlap of the positions of the SC domains at $\theta =0°$ and 15° showing the displacement of stripes towards the right of the image. Right panel: schematic drawing of the Lorentz force $F_L$ on the top surface of the sample, induced by the change in $H_{xy}$ direction.

Figure 4

(Color online) (a) The average angle of the pattern, ${\theta }_m$ (square symbols) as a function of the angle of the applied magnetic field, $\theta$. The dashed line corresponds to ${\theta }_m=\theta$. (b) The number of stripes as a function of $\theta$. Note the abrupt change at $\theta =30°$, where most of the laminae break into shorter segments.

Figure 5

Zoomed-in images of a rotation experiment showing the zigzag instability and the cutting of stripes. The original image is manipulated in order to highlight one particular stripe as the angle is changed. The straight lines indicate the direction of the applied field.

Figure 6

The same as Fig. 5 showing a reconnection event.