Fig. 5: Defect distribution and effect on CO.
a–d Typical topographic images of the Fe3Ge and Ge2 layers of samples #1 and #2, where the native defects are indicated by the black or yellow arrows. The bright spots are residual atoms after cleavage, which have little influence on CO distribution. e Corrected crystal structure of FeGe at 300 K, considering the occupational disorder of Ge1-site. Partial Ge1 atoms (labeled as Ge1b) move in the c-axis away from the Kagome plane, their proportion to the total Ge1-site and the averaged distance from the Kagome plane are ~3% and 0.973 Å for sample #1 and ~2% and 0.865 Å for sample #2, respectively, as sketched in the right panel of (e). f Theoretical predicted 2 × 2 × 2 CO superstructure with large 1/4 Ge1-dimerization, as indicated by the magenta longer arrows. The dimerization strength is defined as the difference of Ge1-Ge1 bond lengths before and after dimerization, \(\Delta d={d}_{1}-{d}_{2}\). \(\Delta d=0\) represents the ideal structure without Ge1-dimerization, \(\Delta d=\,1.3\,{{\text{\AA }}}\) corresponds to the actual value of the CO state. The shorter arrows indicate the small distortions of other sites associated with the in-plane 2 × 2 charge modulations. Possible Ge2-defects (I, II) and Ge1-defect (III) are shown by the sky-blue color. g The DFT calculated energy difference between the CO state and the ideal 1 × 1 × 1 structure for \(\Delta d=\,1.3\,{{\text{\AA }}}\), without defects and with one defect at position I, II, or III, respectively. Measurement conditions: (a, b) Vb = 1.0 V, It = 10 pA; (c) Vb = 1.0 V, It = 300 pA; (d) Vb = 40 mV, It = 300 pA.
