Fig. 3: Br_Te: Scanning tunneling spectroscopy (STS), conductance maps, and two-dimensional fast Fourier transforms (2D-FFTs).

a Scanning tunneling microscopy (STM) topography of Br_Te. b Differential conductance \(\frac{dI}{dV}(V)\) as function of sample bias. The red (black) curve is obtained by averaging the spectra within the circle located at the center (away) from the dopant, shown on panel a. The ranges corresponding to valence band states (VBS), in-gap states (IGS) and conduction band states (CBS) are indicated as green, red, and blue zones, respectively. c Differential conductance map as function of sample bias and distance along a path going through Br_Te center, shown as a white dashed line in panel a. The color bar quantifies the conductance value. The origin of the distance scale starts at the most left end of the white dashed line. The VBS, IGS and CBS ranges are indicated at the bottom. d–f Differential conductance maps at sample bias of 0.07, −0.7 et −0.9 V, corresponding to the CBS, IGS, and VBS, respectively. The scale bar shown on panel f is 3 nm long. As a guide to eye, a plus symbol indicates the center of the image. g–i Maps of the amplitude of 2D-FFTs applied to the conductance maps. Note that the wavevectors coordinates of the maxima are not changing with energy. j–l Maps of the phase of the 2D-FFTs. Note that the phase pattern is changing with energy. The scale bars shown on panels i, l are equal to the length of the reciprocal lattice vector \(\parallel {\overrightarrow{a}}^{\star }\parallel\). m Plot of the amplitude of the Fourier components m_i (continuous line) and \({\bar{{{{{{{{\bf{m}}}}}}}}}}_{i}\) (dashed line) as function of sample bias. Note that the amplitude is large only in the colored zones corresponding to the VBS, IGS, and CBS. n Plot of the corresponding phase for the same components. Note that the phase remains constant in the energy ranges VBS, IGS, and CBS, where the phase value is either a multiple of π or a multiple of π/3. Note the rapid phase shift, indicated by vertical red lines, at sample bias −0.015 V, −0.47 V and −0.8 V, separating the CBS from the IGS from the VBS, successively.