Evidence for Thermally Activated Spontaneous Fluxoid Formation in Superconducting Thin-Film Rings

In a Type II superconductor, the vortex core behaves like a normal metal. Consequently, the single-particle density of states in the vortex core of a conventional Type II superconductor remains either flat or (for very clean single crystals) exhibits a peak at zero bias due to the formation of Caroli-de Gennes-Matricon bound state inside the core. Here we report an unusual observation from scanning tunneling spectroscopy measurements in a weakly pinned thin film of the conven...

A microscopic model is constructed which is able to describe multiple magnetic flux transitions as observed in recent ultra-low temperature tunnel experiments on an aluminum superconducting ring with normal metal - insulator - superconductor junctions [Phys. Rev. B \textbf{70}, 064514 (2004)]. The unusual multiple flux quantum transitions are explained by the formation of metastable states with large vorticity. Essential in our description is the modification of the pairing p...

We report the formation of a pinned vortex liquid spanning a very large region of the magnetic field-temperature parameter space in a 5 nm thick amorphous superconducting Re_xZr (x~6) (a-ReZr) thin film, using a combination of low-temperature scanning tunnelling spectroscopic (STS) imaging and magnetotransport measurements. The nature of the vortex liquid differs significantly from a regular liquid. Analysing series of STS images captured as a function of time, we observe tha...

We present the first measurements of thermal signatures of the Little-Parks effect using a highly sensitive nanocalorimeter. Small variations of the heat capacity $C\_p$ of 2.5 millions of non interacting micrometer-sized superconducting rings threaded by a magnetic flux $\Phi$ have been measured by attojoule calorimetry. This non-invasive method allows the measurement of thermodynamic properties -- and hence the probing of the energy levels -- of nanosystems without perturbi...

We have imaged spontaneously created arrays of vortices (magnetic flux quanta), generated in a superconducting film quenched through its transition temperature at rates around $10^9 K/s$. Spontaneous appearance of vortices is predicted by Kibble-Zurek and by Hindmarsh-Rajantie models of phase transitions under non-equilibrium conditions. Differentiating between these models requires a measurement of the internal correlations within the emerging vortex array. In addition to sh...

The formation and dynamics of topological defects of different structure has been of central interest in the study of the 3He superfluids. Compared to superfluid 4He-II, the variability of the important parameters with temperature and pressure is wider and many features are more ideal. This has made experimentally new approaches possible. An example is the formation of quantized vortices and other topological defects in a rapid time-dependent phase transition from the normal ...

We report the observation of vortex formation upon the absorption of a thermal neutron in a rotating container of superfluid $^3$He-B. The nuclear reaction n + $^3$He = p + $^3$H + 0.76MeV heats a cigar shaped region of the superfluid into the normal phase. The subsequent cooling of this region back through the superfluid transition results in the nucleation of quantized vortices. Depending on the superflow velocity, sufficiently large vortex rings grow under the influence of...

We use neutron absorption in rotating 3He-B to heat locally a 10 micrometer-size volume into normal phase. When the heated region cools back in microseconds, vortex lines are formed. We record with NMR the number of lines as a function of superflow velocity and compare to the Kibble-Zurek theory of vortex-loop freeze-out from a random network of defects. The measurements confirm the calculated loop-size distribution and show that also the superfluid state itself forms as a pa...

We numerically model experiments in which large-scale vortex rings - bundles of quantized vortex loops - are created in superfluid helium by a piston-cylinder arrangement. We show that the presence of a normal fluid vortex ring together with the quantized vortices is essential to explain the coherence of these large-scale vortex structures at nonzero temperatures, as observed experimentally. Finally we argue that the interaction of superfluid and normal fluid vortex bundles i...

We present an experimental study of thermally activated flux creep in a superconducting ring-shaped epitaxial YBCO film as well as a new way of analyzing the experimental data. The measurements were made in a wide range of temperatures between 10 and 83 K. The upper temperature limit was dictated by our experimental technique and at low temperatures we were limited by a crossover to quantum tunneling of vortices. It is shown that the experimental data can very well be describ...