Regensburg 2010 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 2: SC: Applications and Measuring Devices
TT 2.3: Vortrag
Montag, 22. März 2010, 10:45–11:00, H19
Moving a vortex by the tip of a magnetic force microscope — •Ernst Helmut Brandt — Max-Planck-Instiut für Metallforschung
In a recent paper [1] a magnetic force microscope (MFM) was employed to image and manipulate individual vortices in a thick single crystal of YBa2Cu3O7. When the magnetic tip performed a zig-zag motion, wiggling fast along x and moving slowly along y, a large enhancement of the excursion of the vortex end at the upper surface (in the crystalline a-b plane) was observed along y, the vortex path covered an elliptical area with axes ratio max(y)/max(x) ≫ 1. As a first step towards a more detailed theory, we consider the vortex as an elastic string which is uniformly pinned by point defects and is driven by the magnetic force exerted on the vortex near the surface by the tip of the MFM. The tip is approximated by a magnetic monopole and the anisotropy of YBa2Cu3O7 in the a-b plane is accounted for. When the tip moves with wiggles, the vortex is curved and twisted, its motion penetrating to a maximum depth z0 below which the vortex remains rigidly pinned in its straight initial position. Our theory [2] reproduces the path of the vortex end observed in the experiments [1].
[1] O. M. Auslaender et al., Nature Physics 5, 35 (2009).
[2] E. H. Brandt, G. P. Mikitik and E. Zeldov, Phys. Rev. B 80, 054513, 1-10 (2009).