Physikalisches Institut

Abrikosov vortices: pinning and dynamics

The motion of quantized magnetic flux (so-called flux lines or vortices) is mainly responsible for dissipation in superconductors and superconducting devices; this results e.g. in low-frequency 1/f noise. The suppression of dissipation by pinning of vortices using pinning sites and the understanding of pinning mechanisms is hence a major prerequisite for the optimization of cryoelectronic, superconducting devices. One discriminates between natural, intrinsic (e. g. point defects, precipitates, etc.) and artificial pinning sites (e. g. antidots (submicron-sized holes), magnetic point-like structures, etc.

Commensurability effects:

Advances in nanopatterning (e. g. electron-beam lithography) allow the fabrication of artificial pinning sites on characteristic length scales of superconductors. The variation of size, geometry, density and spatial arrangement of pinning sites enables control and manipulation of static and dynamic properties of vortices. The introduction of a periodic lattice of pinning sites gives rise to so-called commensurability effects between the vortex lattice and the lattice of pinning sites. For (rational) multiples of the first matching field B=B1 (providing as many vortices as pinning sites), the vortex lattice is pinned very efficiently. This results e. g. in a enhanced critical current.

Quasiperiodic pinning lattices:

Arranging the pinning sites in a Penrose pattern allows the realization of a vortex quasicrystal. In this arrangement, commensurability effects can also be observed at irrational multiples of the first matching field B1.

Comparing quasiperiodic arrangements with a random or periodic distribution, for properly adjusted pinning parameter one achieve a larger critical current.

Vortex imaging by LTSEM:

We succeded in imaging vortices in high transition-temperature superconductors by means of low-temperature scanning electron microscopy (LTSEM) with a spatial resoution of approx. 1µm. This enables to localize pinning sites and to gain insights into pinning mechanisms for vortices by detailed investigation of the microstructure of such pinning sites. In turn, this allows to improve the properties of electronic superconducting devices and this also provides a deeper insight into physical mechanisms leading to pinning of vortices.

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Publications of our group