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Magnetic imaging of superconducting nanostructures and unconventional superconductors

Domenii publicaţii > Fizica + Tipuri publicaţii > Tezã de doctorat (nepublicatã)

Autori: Voicu O. Dolocan

Editorial: Text in franceza, 2005.


We study the properties of the vortex lattice in unconventional superconductors, using µSQUID microscopy. The most important part is dedicated to the spin triplet superconductor Sr2RuO4. First, we examine the conventional superconductor NbSe2. It is a reference point to the unconventional superconductors imaged afterwards. We observe a hexagonal vortex lattice at low fields, and a rotation of the vortex lattice in respect to the crystallographic axes at higher fields. Next, we present the behavior of vortices in Sr2RuO4. We observe for the first time individual vortices at low fields and vortex coalescence at higher fields.
As the pinning is weak and considering the other experiments effectuated till now in this material, we explain the coalescence of vortices by the presence of domains with different chirality. An important role plays the anisotropy, chains of vortices are observed for tilted fields. We find also that for tilting angles close to the layers, a decoration takes place. These results prove that Sr2RuO4 is an unconventional superconductor with strong anisotropy. In the last part, we present images of the magnetic domains taken in the normal phase of the ferromagnetic superconductor URhGe. We also imaged the individual vortices in the unconventional superconductor UPt3.
We observe a domain formation, this domains being similar with those seen in Sr2RuO4, a parallel between the two triplet superconductors could be established.

Cuvinte cheie: Supraconductivitate -- SQUID -- Supraconductori neconventionali // Superconductivity – SQUID – Unconventional Superconductors