Figure 1: High-resolution STM images for surface modulations at 77 K.

(a) A typical topographic image of IrTe₂ surface taken at 77 K, where a unidirectional superlattice appears on this surface. The setup conditions for imaging were a sample-bias voltage of 200 mV, a tunnelling current of 20 pA with the scan range of 240 × 240 nm². (b) Atomically resolved image of IrTe₂ surface at 77 K, instead of showing a basically hexagonal lattice of surface atoms, displays clear signs of the formation of surface unidirectional modulations. The scan range is 36 × 36 nm² with a bias of −200 mV and a tunnelling current of 0.05 nA. (c) Fourier transform image (upper) of the b and a zoom-in enlargement showing the details of fractional spots (bottom), which displays surface modulations with multiple periodicities of 2.75 × (q₁), 4.22 × (q₂), 7.58 × (q₃) and 9.26 × a₀ (q₄). (d) A series of zoom-in STM images showing the modulations with different periodicities of 2.75 × , 7.58 × and 9.26 × (from left to right), respectively. The surface unit cells are marked by a blue parallelogram, depending on its orientation. The sizes of images: 3.6 × 6.4 nm², 5.1 × 6.4 nm² and 5.1 × 6.4 nm² from left to right, respectively.