Fig. 1: Thermally driven magnetic field step.
From: Generation of ultrafast magnetic steps for coherent control
a, Sketch of the experimental geometry. A 150-nm-thick, 1-mm-diameter YBa2Cu3O7 (YBCO7) disc was grown on an Al2O3 substrate. The local magnetic field surrounding the YBa2Cu3O7 disc is measured by tracking the Faraday polarization rotation of a linearly polarized 800-nm probe pulse, reflected after propagation through a 75-µm-thick GaP(100) crystal placed on top of the sample. A 2-mT magnetic field (Bapp) is applied in the z direction. Its polarity is periodically cycled to isolate the magnetic contributions to the polarization rotation. The colour plot (zoomed-in view) illustrates the simulated (Supplementary Section 7) changes in the z component of the local magnetic field (Bz) induced by the superconductor below Tc. Blue (red) indicates areas with reduced (enhanced) magnetic field, following the colour scale shown in b. b, Temperature dependence of Bz measured above the centre of the YBa2Cu3O7 disc. Each data point represents the mean value ± s.e.m. (smaller than the size of the data points) extracted from a sample of 100 acquisitions (Supplementary Section 5). A clear transition at Tc = 85 K is observed. The measured field exclusion is not complete due to the finite thickness of the GaP detector, which leads to averaging in the z direction (see the main text and Supplementary Section 8). The left inset shows a two-dimensional map of Bz, measured as a function of the x and y positions at T = 30 K < Tc. An increase in the magnetic field is measured near the sample edge (red), and a reduction above its centre (blue). The dashed black line indicates the outline of the superconducting disc. The right inset shows the same measurement at T = 300 K > Tc. No spatial dependence is observed throughout the field of view.
