Extended Data Fig. 10: Atomic structure for two different geometric orientations of the mono and bilayer step edges, highlighting the asymmetry between them.
From: A hybrid topological quantum state in an elemental solid
a, Side view (along the bc plane) of the two monolayer step edges. b and c, Atomically resolved topographic images of the corresponding monolayer step edges along the a-direction. d, Side view (along the bc plane) of the two bilayer step edges. e and f, Atomically resolved topographic images (Vgap = 100 mV, It = 3 nA) of the corresponding bilayer step edges along the a direction. Notably, there is an asymmetry between the two orientations in both monolayer and bilayer step edges, with one orientation featuring a sharper step edge. Interestingly, this preferred orientation alternates between the mono and bilayer cases, in accordance with the even-odd effect observed in the step edge states, where the step edge state appears to favor the smoother edge. We note that visualizing atoms directly at the step edge poses challenges due to the abrupt change in height at that location and the small inter-atomic distance (\(\simeq \)3.7 Å) in α-As. As a result, the atom arrays at the step edge may not be as clearly visualized in our scanning tunneling microscopy compared to those located away from the step edge. g, Extended scanning tunneling microscopy data: Topography (bottom) and the corresponding dI/dV maps (V = −5 mV) acquired at B = 0 T and 2 T. At B = 2 T, the spectral weight at the step edge is suppressed. Such a suppression highlights the impact of time-reversal symmetry breaking on the step edge state. Tunneling junction set-up: Vset = 100 mV, Iset = 0.5 nA, Vmod = 1 mV.
