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(Color online) Lateral imaging of the superconducting vortex lattice in 2H-NbSe2 at various fields and at 300 mK. Panels (a) to (c) show 380 × 380 nm2 spatial maps of the normalized zero-bias tunneling conductance G 0 for fields of 0.09, 0.25, and 0.4 T, applied along the  direction (white arrow in (a)). Panel (d) shows the average G 0 along the direction perpendicular to the stripes in the 0.09 T data. Panel (e) shows a schematic of our experiment, with the STM measuring the ab-surface, across which flows a diamagnetic screening current (red line). In the heuristic model discussed in the text, paramagnetic currents (blue loops) circulating the subsurface vortices perturb the screening current, thus spatially modulating G 0 and producing the observed G 0 image contrast.
(Color online) Separation between the centers of the G 0 stripes, for fields between 0.09 and 0.4 T, plotted on a log-log scale. The data (circles) are fitted to (red line), in good agreement with the expected H −0.5 dependence of the vortex lattice parameter on field.
(Color online) (a) Series of normalized dI/dV spectra measured as the tip is scanned perpendicularly across a stripe at 0.1 T and 300 mK. The midgap states rise over a ≈35 nm wide region, thus accounting for the stripe patterns seen in the G 0 images. (b) Spatially averaged dI/dV spectra over the center of a stripe (red curve) and just between two stripes (blue curve). The zero-field spectrum (green curve) is included for comparison to show the overall effect of the applied field. Over the stripe, the zero-bias dI/dV is higher while the coherence-peak dI/dV is lower, an effect clearly seen in the difference of the two curves, as shown in (c).
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