Master Thesis Effect of vortex shaking on the ... - Physik-Institut

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Figure 24: Comparison <strong>of</strong> runs without and with cycling. The upper figure shows that the velocity <strong>of</strong> cooling did not make a difference. 32
List <strong>of</strong> Figures 1 Shubnikov-Phase (“mixed state”) in a Type II superconductor with the Abrikosov lattice. . . . . . . . . . . . . . . . . . . . . 3 2 Phase diagrams <strong>of</strong> a conventional low temperature and a high T c type-II superconductor. . . . . . . . . . . . . . . . . . . . . 4 3 Visualization <strong>of</strong> the transverse and longitudinal <strong>vortex</strong> <strong>shaking</strong>. In both geometries the vortices drift towards the center <strong>of</strong> the strip. Shown is one <strong>vortex</strong> at subsequent times tω/π = 0, 1, 2, . . . . Top: If h ac is transverse to J, the vortices “walk” in the xz plane (the vortices are straight since here J c ≪ h ac , H a is assumed). Bottom: If h ac is parallel to J, the vortices periodically tilt in the yz plane and at the same time move along x. From [15]. . . . . . . . . . . . . . . . . . . . . . 8 4 Scheme <strong>of</strong> the <strong>vortex</strong> shift in a slab when the longitudinal ac magnetic field is increased from h ac to h ac + δh. Shown is the projection on the xy plane <strong>of</strong> a <strong>vortex</strong> (bold solid line) which tilts more away from the z axis and at the same time shifts from x = x 0 to x = x 0 + δx 0 . The projected shifts <strong>of</strong> some <strong>vortex</strong> line elements are shown as dashed arrows with components δx 0 and δy(z), δy(z) = −δy(−z). These arrows are along the Lorentz force, which is perpendicular to the local current density j c (z) (solid arrows) lying in the xy planes at the angle φ(z) to the y axis. From [15]. . . . . . . . . . . . . . 9 5 Structure <strong>of</strong> YBCO with the CuO 2 planes. In NdBCO the Yttrium atoms are replaced by Neodymium. . . . . . . . . . . 10 6 Location <strong>of</strong> the melting transition in the magnetic phase diagram. (Data from specific-heat measurements.) . . . . . . . . 10 7 Sketch <strong>of</strong> the experimental setup, side view. . . . . . . . . . . 11 8 Example <strong>of</strong> the first unsuccessful measurements at 0 Tesla, where the resistance becomes “negative”. T c is at 96K. . . . . 13 9 Scattered data in the graph <strong>of</strong> the 9T (2/1000/0.1) measurement. 15 10 Results for the measurements <strong>of</strong> the resistance <strong>of</strong> NdBCO without <strong>shaking</strong>. Background and <strong>of</strong>fset distracted. . . . . . . 16 11 Results for the measurements at 7T with and without <strong>shaking</strong>. Upper right: Zoom into the region <strong>of</strong> the melting transition. Crosses representing the run without <strong>shaking</strong>, stars the run with <strong>shaking</strong>. Bottom: Difference between the normal and the resistance with <strong>shaking</strong>. . . . . . . . . . . . . . . . . . . . 17 33
Page 1 and 2: Master The
Page 3 and 4: 1 Introduction The decision to writ
Page 5 and 6: for lower temperatures and a <stron
Page 7 and 8: 2.1.2 The melting transition Let us
Page 9 and 10: on one single crystal the differenc
Page 11 and 12: Figure 4: Scheme of</strong
Page 13 and 14: 3 The Experiment 3.1 Design The exp
Page 15 and 16: x 10 −5 2 0 Resistance in Ohm −
Page 17 and 18: Figure 9: Scattered data in the gra
Page 19 and 20: 0.49 0.48 0.47 0.4345 0.434 Resista
Page 21 and 22: some problems in finding an appropr
Page 23 and 24: 2.53 x 10−4 0 to 7T 2.52 Resistan
Page 25 and 26: Figure 16: To approach of</
Page 27 and 28: Figure 18: Results of</stro
Page 29 and 30: 4 Interpretation and Conclusion 4.1
Page 31 and 32: 5 Appendix Figure 20: In-plane resi
Page 33: Figure 23: Comparison of</s
Page 37 and 38: References [1] J. Bardeen, L. N. Co

Master Thesis Effect of vortex shaking on the ... - Physik-Institut

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