FIGURE 1. Typical gap maps from underdoped and as-grown Bi-2212 samples, each showing an area of 560 Å × 560 Å.

We use an identical colour scale to represent in these two panels for ease of comparison. The colour scale spans the range 20–64 meV, and ticks on the scale are placed at 34 meV, 42 meV and 50 meV. These gap maps were calculated from two 128 128 pixel spectral surveys. a, Gap map of an oxygen-underdoped Bi-2212 sample with T_c = 79 K. This field of view contains approximately 130 compact low- domains which are visible as orange, yellow and green islands against the interconnected blue and black background which are the high- regions. b, Gap map of an as-grown Bi-2212 sample. The interconnected red, orange and yellow low- regions completely dominate the image. Embedded in this environment are filamentary blue and black high- regions. Note that although this sample contains a 0.5% substitution of Ni for the Cu atoms in the CuO₂ plane, the 102 impurity resonances in this field of view affect less than 15% of the area, and furthermore, the local value of does not vary near the Ni impurities⁶. Both spectral surveys were acquired with constant-current normalization in cryogenic ultrahigh vacuum at 4.2 K with tunnel junction resistance of 1 G set at V = -100 mV.