Figure 1. Low-temperature (5 K) STS spectroscopy of as-grown Bi-2201 (AG11 K).

(a) Three-dimensional overview of the data: each curve is the average of 60 spectra sharing the same E_p value (E_p is the peak position for single-peak spectra, and half the peak-to-peak distance for two-peak spectra); the curves are sorted by increasing E_p. Note the smooth transition between completely different curves at extremal values of E_p. (b) E_p map of a 14×14 nm² area. The white bar corresponds to 2 nm. The red and yellow regions correspond to negative E_p (single-peak spectra) while in green, blue and purple regions, the spectra exhibit a gap width of Δ_p=E_p. Red-yellow spots are surrounded by green regions where the smallest gap is measured (∼20 meV). Black patches are composed of spectra (∼4,000 in total) in which no gap could be extracted due to a missing left peak (or sometimes no peak at all); these spectra are not included in the histogram of panel c. (c) Distribution of E_p values. The dashed lines are Gaussian fits. The average peak position and average gap values are −28 and +29 meV, respectively. (d) Spatial evolution of the spectra on the path depicted by the arrow in b. The path goes from a red region (top-most single-peak spectrum) to a black region where the left coherence peak is barely visible. Notice the strong similarity with the global evolution shown in a.