Prof. Yeshurun 6 month visit. Manipulation and control of flux dynamics in high-temperature superconductors and their utilization in fluxonic devices

In an applied magnetic field, the magnetic flux permeates a superconductor in the form of discrete quantised vortices. Their behaviour controls the crucial technological response of the material: the attainable critical current densities. One of the surprises following on from the discovery of the High Temperature superconductors (HTS) in 1986 was that in them, the vortices exhibit a much richer variety of behaviours than in the traditional superconductors, and thus opened up new areas of fundamental physics.Over the last decade, the full complexity of the equilibrium vortex phase diagram has become much better understood, with a lot of attention given to the extreme anisotropy limit, as in the Bi2Sr2CaCu2O8 compound, in which superconductivity is strong within the CuO (ab-) planes, but in the c-direction these planes are only very weakly coupled together. In consequence, in a tilted applied magnetic field, two vortex systems can co-exist in this material: the induction component parallel to the c-axis generates stacks of pancake vortices , and that parallel to the ab-planes forms Josephson vortices. The two vortex systems are distinct, but they do interact both within each system and between systems. Consequently, their dynamics are of great interest too, as exemplified by the recent observation of oscillatory phenomena at Bar-Ilan, and dragging effects in London.In this proposal for collaboration, Prof. Yeshurun will visit Imperial College London, bringing with him some of the samples from Bar-Ilan. During his 6 month stay, we will complement the Bar-Ilan studies (obtained with magneto-optic techniques) with two specialised techniques developed in London: (1) a fast, high-sensitivity imaging facility (based on Hall sensors) that is unique in terms of its ability to operate in high magnetic fields; (2) a sophisticated wide-bandwidth AC susceptibility rig, in which the applied field components parallel and perpendicular to the CuO planes can be controlled independently, and be energized with a variety of waveforms.We will first look in London at the crystals brought from Bar-Ilan that exhibit the oscillatory phenomenon to establish a cross-assessment between the two sets of techniques. We will then look to see whether on different time-scales, or with other different conditions, the phenomenon occurs in a wider region of field-temperature phase space.The fact that these interactions can be used to cause flux to move suggests that fluxonic devices might be feasible utilising this approach. In the second half of the 6 month visit, we will explore patterning the samples to better engineer useful architectures.Finally, we regard the visit as a key opportunity to further the collaboration between ICL and Bar-Ilan on vortex physics and potential fluxonic devices.