Fig. 2

QPI measurements on RbFe₂As₂. a, b Representative dI/dV maps taken on type A surfaces. The mapping area is the same as shown Fig. 1a. c, d Representative dI/dV maps taken on type B surfaces. The mapping area is marked in Fig. 1b. (Scale bars in panels a–d: 10 nm) e, f Representative raw and symmetrized FFT images of the dI/dV maps taken on type A surfaces, respectively (scale bars: 0.3 Å⁻¹). g, h Representative raw and symmetrized FFT images of the dI/dV maps taken on type B surfaces, respectively (scale bars: 0.3 Å⁻¹). The orientation of the unfolded BZ is marked on the first FFT image of panels e and g. i Sketch of the unfolded Brillouin zone of RbFe₂As₂ and its relation to the FFT pattern. The C₄ symmetry breaking makes (π, π) and (π, −π) inequivalent. j FFT profiles along (π, 0) direction of type A surface (averaged over a 30° angle that indicated in panel f), in which a hole-like dispersion can be observed. Parabolic fit (white dashed curve) gives E_b = 27 meV and q_F = 0.21 Å⁻¹. Another hole-like dispersion (black dashed curve) slightly below E_F is observed. k FFT profile of type B surface along the (π, π) direction (averaged over a 30° angle indicated in panel h). l FFT profile of type B surface along the (π, −π) direction (averaged over a 30° angle), another hole-like band can be seen below E_F. Note: All QPI data are taken at T = 20 mK (T_eff = 310 mK). The symmetrized FFTs are mirror symmetrized along (π, π) and (π, −π) directions (see Supplementary Note 3 for more details). Each dI/dV maps are taken at a V_b equal to the mapping energy (labeled) and I = 100 pA; the lock-in modulation (ΔV) for each map has an amplitude of 5% V_b