Figure 1

Principle of the experiment: laser light creates a normal conducting hot spot $hs$. The current induced by the periodic heating causes a voltage drop between the detecting point contact $pc$ and the reference contact $r$ when it passes a normal conducting domain $n$. When passing a superconducting domain $s$, no voltage drop occurs. Thus, in position 1 a signal $V$ is measured and in position 2, $V$ will be zero. In the experiment, the optical fiber $f$ is moved to obtain spatial resolution while the point contact $p$ is kept in a fixed position.Reuse & Permissions

Figure 2

Imaging of ring-shaped vortex domains in Nb: Left: gray scale representation of the signal $V$ as a function of $xy$ real space coordinates on the sample surface. The applied magnetic field is $B=0.1\mathrm{T}$ perpendicular to the image plane. Image frame: $800\times 800\mu \mathrm{m}$, $60\times 60$ measured points. The gray scale ranges from $-220\mathrm{n}\mathrm{V}$ (black) to $-115\mathrm{n}\mathrm{V}$ (white) measured between the point and reference contacts. A normal conducting vortex ring appears around a sharp peak. The sharp peak is due to the normal conducting heated region (”hot spot”). Right: perspective representation of the same data.Reuse & Permissions

Figure 3

Numerical simulation of vortex ring creation: in each panel (a) to (d), the left side (blue background) shows the temperature distribution, whereas the right side (red background) shows the distribution of the order parameter (red: 1, blue: 0). The initial topological charge was 16 and the radius of the hot spot $4\times {10}^{-5}\mathrm{c}\mathrm{m}$, the diffusion coefficient was $0.009{\mathrm{c}\mathrm{m}}^2/\mathrm{s}$. Time evolution at (a) $t=0$, (b) $t=2\times {10}^{-9}\mathrm{s}$, (c) $t=1.2\times {10}^{-8}\mathrm{s}$, (d) $t=5\times {10}^{-7}\mathrm{s}$.Reuse & Permissions